I don't think rapists should have parental rights, but proving rape is often problematic. We often think of rape the way it's portrayed on t.v.: a stranger jumping an unsuspecting woman as she walks home in the dark, or who breaks into her home while she is sleeping. But 50% of rapes are committed by someone the woman knows. Sometimes it's a boyfriend who, when they are making out, doesn't stop when the woman says no. A jury is then left to decide between the story the woman gives versus the story the man gives. Some rapists have offered the argument that the woman's vaginal bruising is due to the fact that "she likes it rough." In one case, a lawyer argued that the bruising could have occurred from having a number of sexual partners within two or three days' time.
Because of some of these he said/she said cases, and instances where rape victims are not taken seriously when they do report crimes, and because many women don't want to relive their experience through court testimony and police reports, many rapes go unreported. So it's a nice concept, but realistically, it won't solve the problem for many rape victims unless you eliminate due process for accused rapists, which isn't fair either.
Given the nature of the situation, I almost think the parental rights of a father should have to be earned. If you impregnate someone, you have a duty to financially support that child, but if you walk away (or run away!) from the child's mother when you find out she's pregnant, and leave her with the bills and the care and raising of that child, and some years later decide you want to be a part of that child's life, your rights should be considered as abandoned right along with the responsibilities you shirked.