Voluntarism is another word for the notion that it does not matter if x is really right or wrong it is made right or wrong by whatever you or somebody wants to think about it.  For most voluntarists, it is about what God wants to think about it.  Even they admit that a voluntarist may be doing this just to pass the buck to God when it is himself or herself who is really concocting the morality.  Even if it were possible to be voluntarist without just trying to avoid responsibility like that (it isn't) we never know.  It does not matter anyway who does the commanding if morality can be that cheap and that "inventable".  So the emphasis on God would be absurd.

So suppose God is a voluntarist.  Then abusing a child for fun can be a saintly act in God’s (or anybody's) scheme of things.  God just has to say it is good and it is.  For some, this means that God in some hidden way is able to make it good in reality.  That would mean if we seen the whole picture we would understand why its right.  So it is not really abuse in this scenario.  For the rest it means that no matter how much pain it causes and if God's aim is to see the child hurt child abuse is right if he says so and for no other reason.  Its not about consequences.  This the purest voluntarism and the most common among believers in God.

In theoretical terms, there is a difference.  In terms of uselessness there is no difference at all.  You may as well just flip a coin.

Islam is a voluntarist religion in the purest way. Most Christians are voluntarist that way as well even if they do not realise it. A voluntarist God is dangerous. But Christians are able to reject this God and create one that may as well be voluntarist.  If you create doctrines about God on your own authority and by your own ability then even if you are right you are not right because you respect God or truth.  The author who is right on who the Ripper was and why but out of luck does not really know for sure and is talking about his own opinions.  A God of man's opinions is not a God at all.  So you can be voluntarist despite repudiating voluntarism.  You can be voluntarist in spite of yourself.  A God worshipped by human speculation and opinions and which is a product of them is voluntarist by definition.  Napoleon is dead.  Read all you want but you don't know him even though you feel you do.  So it is with a God who is seen through whatever lenses you set up to look at him through.  You don't see him as such.

Those who point to how the abuse of a child results in bad outcomes and who list them and come up with morals that humanists would agree with might appear to be taking morality seriously as being about benefiting people.  Are they really?  A voluntarist whose moral code just happens to agree with the real moral code is still a voluntarist.  A mathematician who guesses the right answer to an equation and is right is acting as a guesser not a mathematician.

It is voluntarist to make God the source of morality for you volunteer to decide that there may be a God and volunteer to say he is a moral authority and volunteer to say what that morality is and what it entails.  That is a lot of different volunteering.  Even when you don't deliberately or knowingly make a voluntarist God you are making one.  We are talking about you as a voluntarist.  It is even more voluntarist of you to intentionally devise a voluntarist God.  You are using God to hide that this is about you not him so if your morality bans such manipulation you are violating it.

Voluntarism is just lazy and disgusting.  If you decide that nothing is really wrong then why bother trying to influence others with your morality?  Morality if real and if it is good and true simply has to get you to influence others.