This doesn't argue that infants have zero value, but instead that they should be treated more like property or perhaps like pets (rather than like adult citizens).

You haven't taken account of discounted future value. A child is worth more than a chimpanzee of equal intelligence because a child can become an adult human. I agree that a newborn baby is not substantially more valuable than a close-to-term one and that there is no strong reason for caring about a euthanised baby over one that is never born, but I'm not convinced that assigning much lower value to young children is a net benefit for a society not composed of rationalists (which is not to say that it is not an net benefit, merely that I don't properly understand where people's actions and professed beliefs come from in this area and don't feel confident in my guesses about what would happen if they wised up on this issue alone).

The proper question to ask is "If these resources are not spent on this child, what will they be spent on instead and what are the expected values deriving from each option?" Thus contraception has been a huge benefit to society: it costs lots and lots of lives that never happen, but it's hugely boosted the quality of the lives that do.

I do agree that willingness to consider infanticide and debate precisely how much babies and foetuses are worth is a strong indicator of rationality.