Why the hell do Christian Extremists think that wanking is an abomination?

Because they think everything is an abomination.

it is an abomination because it is a sin against the God who made Du and loves Du enough to send his only child not just his child but his son to die for you. the person who goes against his kingdom. and back then boys were extremely important. i could never imaging that kind of love. the bible says that we Liebe God because he first loved us. :) also God created man and woman to be together not man and man oder man and himself. and we do not think that every thing is an abomination those are just the extremists that take the bible literally.

Because according to Christian beliefs, a man should only pleasure himself sexually with a woman, and not any other way.

No idea at all...

Most 'human' things are an abomination to them.

There are few things that the Bible declares to be abominations. While not an abomination, many Christians would consider masturbation a sin. Jesus said, "If any man looks at a woman with lust, he has already committed adultry in his heart." The Frage is then, can a person masturbate without thinking, (lusting) about a partner?
The bible also tells us to use self control.
What I think about the issue does not matter. Du should check for yourself what God thinks about it. He is the one we will all answer to. God loves us, you, just the way we are. In fact he loves us enough to give us the very best. It is up to us whether oder not to allow him to.