A pre-coitus agreement between two sexual partners is, in fact, an interteresting idea. The problem is that it really wouldn't work out, in practice. Too many heterosexual couples would willingly jump into bed together without discussion of the potential outcome & responsibility of parenthood.

Similarly, the legally-binding paternity waiver you propose is also an intriguing idea. But how many couples are just going to ignore the possibility of signing one? Also, once a pregnancy happens, what do you do about physical or psychological circumstances that may change -- from one or both biological parents -- which would be a hinderance on their ability to provide and parent?

The implications of a potential pregnancy that a man and a woman SHOULD discuss before sex are all very valid. Again, "should" is very idealistic...very aspirational...and very theoretical. And yes, the discussion may be uncomfortable for them. But talking about sex is uncomfortable for all kinds of couples (including those who are unable to conceive children). From my own experience: I'm a "side," in terms of my own romantic/sexual life...so, even though I am gay and the pregnancy risk is zero within the context of my love life...if I was a heterosexual male "side" (I know, you'd think they'd be very rare), my risk of impregnating a woman would also be virtually 0%, under those circumstances. Maybe unmarried straight couples should consider the idea of "side sex" themselves, as a family planning option? At least until they're officially married?

The point, here, isn't to get the government involved in people's lovemaking choices. It should be to provide options that will maximize a healthy outcome for all parties involved -- including the unborn / newly-born child. Legally treating the biological father like a human-sperm-dispenser-followed-by-an-ATM-machine normally wouldn't achieve that end.