The Roman Catholic Church claims that sprinkling water on a baby or an adult while saying, "I baptise you in the name of the Father and of the Son and of the Holy Spirit" does amazing things. It takes away the sin we are born with, original sin, and any other sins and grafts us on to Jesus making us his servants. It puts Jesus and God inside us to live in us and inspire us. The Church says that baptism heals the inclination towards sin that original sin causes. Baptism is a sacrament. It pictures cleansing from sin and the effects of sin and actually does what it pictures.

The National Secular Society in the United Kingdom issues De-baptism certificates. These are used by people who renounce their baptism. Those people may also choose to have a note added to the Church registrars to the effect that they have left the Church and are not to be counted as members anymore.
The de-baptism certificate holders claim to undo not the fact that a ceremony of baptism was administered to them but the obligations conferred by the baptism. In other words, de-baptism is about renouncing any effects and duties related to baptism and about renouncing membership in the Church. It is shaking off the rights the Church has over you by its law. Catholics yell, "But if you don't believe our Church really has authority from God and that its authority is illegitimate then why should you care? Why get de-baptised when you don't think baptism had any effect and was just hocus pocus?" But if you say the Catholics are secret pagans and therefore members of your pagan cult would they like it? They would denounce you. So why let them say you are Catholics when you strongly don't want to be and feel you are not? Why should they get special rights? But the Church law is still law. Catholics hold that we are bound to it. To say you can ignore Catholic law if you don't believe in it and were baptised Catholic is a denial that it is a law at all. The Catholics are so anxious to deny that people leave their fold that they would say anything.
Some have ridiculed the practice of De-baptism on the grounds that the fact that if you were baptised then your baptism is a fact and still happened. But the ceremony may have happened but that does not mean any genuine baptism took place. The ceremony is only outward but you can't see the power it gives. It may not even give those powers - for example, if the priest serves the devil he may not intend the blessings of baptism to be transmitted to the child. Then though the ceremony has taken place no genuine sacrament of baptism has been administered. If a genuine baptism does not take place, then no genuine initiation into the Church takes place. The result is a person who may only imagine they are real members of the Catholic community. Obviously there is no way to test if a person is really a member.
It is not really baptism, strictly speaking, that has the alleged effects. The Church believes that baptism is a sign that God is working in the person. The water and the ceremony have no power in themselves. It is just that God has decreed he will work when the ceremony is done. That is what the Church means when it says that if the priest baptises then strictly speaking it is really Jesus who baptises or God.
It is really the initiation conferred by baptism that needs to be reversed. The baptism itself is only a sign that God and the Church are possibly initiating a child. I say possibly because God does not confer valid baptism if the priest intends it to be a pretence. Rather than de-baptism the emphasis should be de-initiation.
The Church believes babies have no sin they have committed themselves but they have original sin - an inherited rejection of God. If that sin keeps them out of God's community and reversing it puts them into the community then surely a baptised person who sins greatly is not a true member of the community? They are more hostile to God than any baby could be and they know what they are doing! Then the baptismal grace is totally ruined. One would need to be baptised again to get it back but God settles for accepting the original baptism instead of requiring that. In your heart you are being rebaptised. That is what the Church means when it says you must live out your baptism every day.
De-baptism should be about renunciation of the meaning and effects of baptism. It should be about retrospectively making the ceremony null and void.
If you really had original sin as a baby then it follows then that left to yourself you would renounce God if you were developed enough to know what you were doing. You can't consent. But original sin inclines the child to want to do evil and do good without reference to God. Without consent we have to go by the nature of the child. If the child has original sin then that has to be treated as consent not to be baptised. Infant baptism then is a powerless ceremony. It has no binding authority.
It is very sly of priests, especially Catholic priests, to have parents bringing babies to them for baptism when those parents are not making an informed decision. There is no discussion about the problems of baptism. The parents are only given the Catholic side of the story. Catholic priests make incredible claims for baptism, stronger than that of most Protestant Churches, which is why I refer to them as especially manipulative and sly. They say baptism is the biggest step in life for the child and yet they don't act consistently with this assertion. They are like suitors who wish to rush the women they want to marry to the altar before the women can think about it properly.
If the priests were honest enough to be blunt and to say, "Your baby is a bastard and it doesn't belong to God but we can fix that in baptism. God doesn't have a relationship with it for it has original sin", many people would think twice. It might sound unkind for priests to be that honest. But if what they teach about baptism is true then it is not.
Baptism is intended to marry the baby to the Church. If that is not a null wedding then nothing is!
The Church says that a mark is put on you by baptism. If baptism has power, all the power can be rejected and renounced. When that happens, the baptised person is in the same situation as an unbaptised person except that there is a mark. What is the mark for? It is a sign that the baptismal power can be reactivated and retrieved if the person repents. The person might have been physically baptised but physical baptism is a symbol of spiritual baptism. The spiritual side is really what it is all about. If that is all renounced, then the baptismal effects have been undone. Only the mark and the fact that a physical baptismal ceremony happened remain. But you are effectively de-baptised.
Your choice with regard to religious membership when you know what you are doing takes priority over any choice made by your parents and godparents to enter you into such membership. A choice made for you cannot have the same force as one made by you. Your personal choice matters most. So if you reject the religious membership that baptism gave you, you should be annulling your baptism. God is almighty and nothing can violate his will not even the sinner for God then permits the sin to happen. So God knows if a baptised baby will accept the choice made for her or him. Seeing a rejection means that God will have to regard the consent of the godparents and the parents as invalid and not impart membership of the church on you.
De-baptism can be seen as a declaration that though a ceremony happened it was just mumbo-jumbo and you are unwilling to be listed as a member of a Church over it. However, a baptism annulment certificate would make more sense and be a better idea. It is clearer.
A revision of a post I put on Reuters re Dutch Catholics trying to de-baptise themselves.
De-baptism? A more sensible thing to do would be to try and see if you can declare your baptism null and void even according to Church Law.

Lots of priests are modernists - ie secret liberals who believe Jesus did not found the Church or start Catholic baptism. Thus they cannot intend to baptise as the Church does - and the Church is clear and certain that baptism without that intention is not real baptism and is a waste of time.
The CDF in the Vatican declared that Mormon baptism is invalid for Mormons hold that baptism was not established by Jesus Christ and claims it gives the baptism of John the Baptist. The Church argues that to baptise validly you must intend to do what the Church does - ie intend to give the baptism Jesus instituted. But Mormons hold that the baptism was established in Adam's time and they intend to give the baptism of John though they use the Christian wording for the rite. Fr Luis Ladaria states, "According to the New Testament, there is an essential difference between the Baptism of John and Christian Baptism. The Baptism of the Church of Jesus Christ of Latter-day Saints, which originated not in Christ but already at the beginning of creation (James E. Talmage, Articles of Faith [AF], Salt Lake City: Desert Book, 1990, cf. pp. 110-111), is not Christian Baptism; indeed, it denies its newness." If the Mormons do invalid baptism, the modernist priest does baptism that is ten times more invalid!
The Bible is supposed to teach that anybody who got John's baptism needed to be rebaptised for it was not the baptism of Jesus even though John's baptism was about Jesus.
Acts 19:1-7 While Apollos was at Corinth, Paul took the road through the interior and arrived at Ephesus. There he found some disciples and asked them, "Did you receive the Holy Spirit when you believed?" They answered, "No, we have not even heard that there is a Holy Spirit." So Paul asked, "Then what baptism did you receive?" "John's baptism," they replied. Paul said, "John's baptism was a baptism of repentance. He told the people to believe in the one coming after him, that is, in Jesus." On hearing this, they were baptized into the name of the Lord Jesus. When Paul placed his hands on them, the Holy Spirit came on them, and they spoke in tongues and prophesied. There were about twelve men in all.
Modernist priests often believe that John established baptism for Jesus never intended to create a Church though Jesus got his disciples to give the baptism of John. Such then cannot give true baptism for they are even further away from Catholic belief than the Mormons.

Lots of priests are atheists or believers in something different from the Catholic God. Modernists use religious language in a symbolic way. The CDF said that Mormon baptism despite being done in the name of the Father, Son and Holy Spirit was done with the intention of denying the three in one God and so was invalid. It follows that a modernist priest whose theology of God may be even more unChristian than the Mormons cannot validly baptise. Its only a ceremony with no effect. It does not make the child a member of the Church like valid baptism allegedly does.

If you have reason to believe the priest who baptised you was a modernist at the time, then the baptism was invalid for he broke the Church rule "a valid baptism must always be performed with the intention to do what the Church does."

Finally if baptism really puts God's power and grace in you, you will know that. If you can't perceive it then clearly you have proof but only to yourself that your baptism did nothing supernatural and was not real and thus you never were a real Catholic.