Ok, female input. I have issues with this as a female because, you're right in that its your body and its your choice, and not everyone agrees with abortion. However, you call it his 'mistake' girl it ain't just up to the man to put something on it..everyone to the man, and to the female has a responsibility to use contreception if they don't want a child, and if you don't and you get pregnant and you chose to keep the baby, then that is your choice. Lets be honest if a 'mistake' occurs the man actually has no say...he isn't the one who is pregnant, and he can't physically make the choice, only the women can do something about it. If men were the ones who got pregnant, things might be a little different...and after all, you said it, it is half his DNA.
If, lets say you and your man are together and you've been together for a while, you have a child, it wasn't planned but you both wanted it anyway. Then two years down the line you split, and he decides he don't want anything to do with the child, he don't want to pay for it, and he don't even want to see it. Then yes, I would say in this case senario he needs to take responsibility for his child because when it was concieved he was happy for it to go ahead. and yes I believe he should pay what the goverment says he should.
But some girls, and it does happen, get pregnant, have the child, despite the guy not wanting it, and then force and complain that this guy isn't doing his duty for his child. I am not a feminist, but I do feel that, if a mistake occurs and (actually its not a mistake if you didn't use anything, because well that's what happens when sex is unprotected) But I do feel that, because the guy can't actually physically do anything about it, that the girl is actually trapping him into this by having it. Where's the men's rights? why should men be trapped into something they have no control over in any way.
i actually think men should have the right to decide in cases where, it was a mistake, they're no longer with the girl, it might have been a casual thing, or one night stand, to whether they keep it or not, because just because nature gave it to the woman to carry, doesn't make it her god given right to tell men they should then take responsibility for it. And if the case is it was a mistake, the guy don't want it, but the girl has it because she wants it, then no, I don't think men should pay. Because the man as I have already pointed out, cannot physically do anything about it.
Sorry but, the baby thing is so much more complicated then how you make it.