I'm definitely not a lawyer, and not even having been married I can't say I have experience with how it exactly works. I'm trying to put myself in the mind of non-paying fathers and see what they might be thinking, since most people are inclined not to give them the benefit of the doubt. All I could come up with as legitimate reasons were:
1) This never should have been my problem - which is where my comment about abortion came from, and its a valid thing for someone who asked for an abortion to think, especially since men are required to defer all their rights in this area to women.
2) "She stole him from me." -I bet this is thought quite a lot, and in some cases its probably a valid since our legal system is biased towards women when it comes to parental rights.
Actually I bet both of these thoughts go through support-paying parents minds quite a bit, though realistically most cases its probably not valid. (Did you really tell her to get an abortion and she refused? Did you really do nothing to deserve loss of custody?) I only bring it up because non-paying dads get about as much sympathy as murderers, and in some cases they most likely deserve more than that.
The whole topic really points more to me about how broken marriage is in general. It seems almost routine that parents will have to decide custody of their kids at some point, and it will undoubtedly be nasty and leave bad feelings for both parents and the kids involved.
Maybe this is a consequence of the "looser" sex and easier-to-terminate marriages that came along with woman's lib. <pause> I can feel the hellfire coming down already so let me explain... I do not mean to say that women's lib is or was a bad thing in general, I'm rather saying that as women became less dependent on men, divorces became something they could realistically seek. Like any major social change it would naturally have both positive and negative effects. In this case the definite upside of getting women out of bad to devastatingly-bad relationships, but the downside of weakening the durability of families. (This idea just came to me while I was typing the previous paragraph, I'm not desperately attached to it. Anyone have any opinions? )