[alnorth]

Look at it from the state's point of view. As a matter of public policy, we have decided that if you have sex with a woman and knock her up, then you are the father, and entitled to parental rights and financially responsible, with some odd exceptions like rape. As a matter of public policy, we have also decided that fathers and mothers can not waive financial responsibility, unless the kid is adopted out.

Whether you agree with it or not, thats the case. OK, since that is the case...

if you don't go through a clinic or a doctor, how is the state supposed to know whether or not you had sex? As far as they are concerned, you might be lying, and maybe the woman is helping you lie in exchange for sole custody. Even if she claims to be a lesbian, maybe she's bi, or drunk, or whatever, the state doesn't want to hear it.

There's a procedure that must be followed to be a sperm donor. If you don't follow that procedure, the state is just going to assume you knocked her up.