So it makes an absurdity like ‘a woman who can’t produce sperm is the same as a man who can’t produce sperm’ seem feasible.
I agree that it is quite absurd. In many ways.
But I think from the point of view of a woman who is receiving fertility treatment to conceive a child, then the problem is a partner who cannot produce sperm. It is really an individual woman being treated in these situations, rather than a couple. Even if we pretend otherwise.
Logically, choosing to not treat the lesbian but to treat the straight woman is a decision based solely on her sexuality.
Now, whether that is reasonable or not is a different question and people will have different views. Some people will take the view that any woman who wants to become pregnant but whose chosen partner can’t facilitate that should receive fertility treatment. Others will want to consider the differences between a male partner who should be able to produce the required gamete but cannot due to dysfunction of his reproductive system and a partner who simply would never be able to produce the required gamete at all.
And, as you say, there is an argument potentially that lesbians know they need to find a man if either of them want to conceive a child. But, equally, it’s conceivable that women whose partner is infertile could be told to find themselves a different man who can produce the required gamete.
Gay men are an entirely different thing because neither of them can be treated to produce a pregnancy. One of them can donate sperm to the process, which is a pretty limited ‘treatment’. They require another woman to be treated so she can conceive and then gestate a pregnancy. It’s just not comparable.
No clear answers there, but it’s not simple and does really require a proper discussion that doesn’t start from the idea that all adults are entitled by right to have a child (produced to order) regardless of any biological factors.