If a woman intentionally deceives a man about her birth control measures, I do not think the man should have any responsibility for the child, assuming there is some sort of proof of the accusation of deception. Anyways...
From a utilitarian perspective, the justification of child support is simple. Class systems make it so a parent's economic value is the main determinant of the child's present and future economic value, as the statistics show.
A single-parent home can raise a fine child, there is no doubt - but you are essentially shifting the economic burden of the child from the parents, onto the child. What college they attend, what sports they can play, what teachers and health care they can have, and consequently their entire lives... that all depends on their parents, one of whom will no longer have any financial responsibility on the grounds that the other could have had an abortion.
From a logistical perspective, abolishing child support on the grounds that the man didn't want the child is difficult as hell. If a man does want the child, then decides eight months in that he doesn't, does he have any responsibility then? How about after six months of pregnancy? How about after three months? When does a mans financial culpability for a child begin, if not conception? If he wants an abortion, should he have to pay for half? If he doesn't, should he still have to pay?
The essential truth is that child support is the only way to make freedom of choice possible, for man or woman. If a woman wants a child, has it, then takes off, she should pay child support. If she didn't want it but had it anyway, then takes off, she should still pay. Men should face the same standards. That is fair.
Our biology does not allow true equality. Women must be in control of the fetus, and both men and women must pay for their child. Any other perspective requires obscene laws, and causes far more harm than it prevents.
That which causes the least harm is the fairest.