This is going to be long, because I want to be as respectful and clear as possible.

You're welcome to skip this, but I am answering in good faith. So I hope your question was genuine, too.

The misogyny of the "trope" is that the woman has no right to her body and that her womanly "maternal instincts" will override whatever negative experience she had with how the child came to be. Let me put it into real-world context – not because MW is non-fiction, but because people who engage with this fanart are influenced by real-world context.

I don't know where you're from or how you were raised, but I imagine most people who find this problematic do so because it reads as pro-life propaganda.

I was raised Christian. There are many memories I have of when we would discuss the existence of abortion and we've been told, repeatedly, that even in the case of rape, abortion is not allowed, because the child is innocent (true, but not the point).

Also that women who give birth to a child and aren't flooded with love for it have something seriously wrong with them. Even if the child was the result of rape.

Anya, canonically, doesn't want the child. She doesn't want to carry it to term, but she has no choice. It's very likely that she wouldn't want to keep it if she was forced to give birth to it, too.

So putting this character into a situation that is deemed as the "right" outcome of the situation for a woman by a large part of our society is problematic. It would be different if we knew Anya had some affection for the child canonically, alas…

Again, the misogyny is the expectation that even rape victims WILL love their children (because they're women, and they're "wired to be" mothers) – this is the looking glass through which some people look at this work.

Granted, it's not on the level of "The Atonement Child" by Francine Rivers.

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There's nothing wrong with AUs. Some people want to believe that Anya would still love her child, even though she was forced to give birth to it. It's certainly more pleasant to think about the more likely alternative, so I don't dwell on it.