I'm not going to argue about the case where the couple agreed nothing beforehand (since I consider the "default view" in lieu of such agreements, though unfair, to be far less important if op-out arrangements exist) nor about cases of rape (in which I'm sure nobody would dispute that the rapist should get the worse end of the bargain). However, on the areas I do argue:
Counter-Arguments:
She's being allowed to "wriggle" out of it because the contract concerns the child and what it needs and dare I say what it's "entitled" to so to speak and she can't give that away in the first place, especially before it's born.
Let's look at the logical consequences of this view.
Scenario A: Woman A steals Man B's sperm. Woman A gets pregnant. Woman A sues for child support.
By your lights, in this scenario A has the right to child support from B as the child is entitled to child support. Despite this, A has control over how the money is spent (for the most part) despite it being B's money. The only way to get out of this is to say that Man B's consent to take on a potential obligatoin comes into play. In this scenario, Man B has waived said obligations with agreement.
So what if people are worse off than them in their own country or in Africa or on Mars? So the solution when faced with possible harm is to point at poorer people, shrug and walk off?
As for responsibility:are you challenging the idea that the man is responsible for the child he spawned at all? Because that's the only argument I see.
Let's look at this logically. I'm going to assume you reject the Peter Singer-esque view that everybody in this world has responsibilities to help everybody else in need. If this is so, then it follows that EVERYBODY should contribute in supporting the child if they need it but that nobody should if they don't.
Thus, you are going to have to maintain the view that a father has special responsibilities to support their child. Under normal circumstances I would see a decent case for this- the man has agreed to take on a responsibility because he knew full well the responsibilities of his actions. However, in this scenario he waived said responsibilities and the woman agreed, thus implying intention either to raise the child herself or abort. In effect, the man has let the woman take over full rights regarding the child.
You can't say that a man is responsible to their child because they are the father of the child, regardless of anything else, or else you would have cases involving child support and rape or stolen sperm. Either you must accept that raped men can be compelled to pay child support, or you accept that a child's right to life support is limited. I would argue the latter- a father's special responsibility to their child only comes
Scenario B: Woman A and Man B have sex. Man B is sued for child support. Later on, Man B wants to commit suicide. He has an income but not enough assets to pay substantive amounts of child support.
Do you say that Man B can be forced to stay alive and work to support the child?
(EDIT: I just thought of the possibility as I was finishing that you might argue that a man should be forced to take responsibility because the child was created by their actions, analagous to how those who create messes should be obliged to clean them up. The problem with this is that the woman is NOT forced to take responsibility if they don't want to.)
Arguments:
The following is my guesswork as to your posistion:
-Peter Singer's claim that people are obliged to all those in need is a false one (or else the needs of children in Africca would come first).
-A child has an inherent right to child support from both parents.
-This right comes about because the child was brought into being by their parents and needs help to get started in the world.
(It can't be simply because children need support or you could advocate the government stepping in instead, and Third World children, or the children with the lowest material living standards regardless of parental status, would have first priority)
-These rights do not extend to emotional support (or else you could morally force parents to stay together for the sake of the child).
This is a very strange sort of right. You cannot say that the child's right to support comes simply from their parents being their parents (or else you would have to agree with raped parents paying child support), you cannot say the child's right is because they need the money (or else you would have to agree with Peter Singer), and you cannot say the child's right is because their parents took on an obligation (as they have waived the obligation in this case).
You could try to say that it is
inherent in natural law that if a father brings a child into the world of his own free will he must support it. However, the problem with this is that in a pure "state of nature" (not the theoretical state of nature, but a Stone age tribe of Homo Sapiens bereft of civilisation), the father would gain rights of rape and dominance over the woman in exchange even if he were compelled to look after the child. If what is natural is just, you have to accept the father's rights as well (which in this case I am sure you will not do).
Furthermore, take a final Scenario C.
Scenario C: Say A and B have sex and have a child. By mutual agreement they give it up to a third party, C. C is a single parent. A and B, let's say, no longer have to pay child support. Is this unjust?
If you say it is unjust, you are advocating for a considerable amount of law reform. If you say it isn't, then why is this scenario any different? In both cases the child has support from only one parent.