How can an all-good God let evil happen and let innocent people suffer horribly? He has the power to stop it.
If God is all good and all powerful then it follows that if he exists, then suffering must happen for a reason. He lets it happen for a purpose that makes it right to allow it.
Religion claims that the general principle is that suffering must be a part of life. If we did not suffer we would not be alive.
It does not believe that at all. It says God does not suffer and he is alive. It says we will be free from suffering in Heaven. And it is not true that even if life requires that you face pain it does not follow that life requires that you may face suffering. Suffering is needless and useless.
Pain and suffering are not exactly the same thing. You can feel your existence is worthwhile to whatever degree if you have pain. Suffering is a form of pain that makes you feel your existence is not worth it. If God can allow pain, it does not follow that he can allow suffering. Suffering would mean he has given us the faculty to feel that our lives are useless and that if he has a purpose for us it means nothing for us.
Suffering is the experience of meaningless existence - it is experiencing something that tells you you should not be happy or alive.
How can God be called good when people suffer? He is able to stop it but refuses. He makes the brain and nerves that have the power to create suffering. It is nonsense that God does all he can to help us have an ultimate reason for living. One person who believes life has no meaning may still be reasonably happy. Another reacts a different way. The feeling of despair takes its grip. The reaction then totally depends on how the person's brain and nerves are. It is not the belief that life is useless that does it. If God makes all things then God is to blame.