I don't see the direct connection between trying to limit certain people's access to dangerous weapons and laws that determine who can and can't have kids. Although limiting the ability of crazy people or criminals to have kids may not be such a bad thing. In any event, I think the right to own a gun should be limited to those who are not criminals and do not have diagnosed mental issues. I don't think either of those would have protected the people that got shot by Loughner, though. He was not really a criminal (except petty vandalism) and it doesn't look like he'd been diagnosed yet.
Reading the posts by Songline, Hockeymom, Missizzy and Nova, one can really see the dilemma. Do we allow for involuntary treatment or assessments based on the say so of relatives, or some sort of authority like college admins etc.? Do we allow for involuntary long-term lock-up of persistently mentally ill people who won't stay on their medications? What about all the abuses that occurred when such was allowed? How husbands and fathers used the laws to control women? How certain people seen as non-conformist were subjugated by such laws? And yet, I hear of so many horror stories from people watching their loved one suffer or suffering as a result of uncontrolled nuts that are free to harass them.
My roommate's mom and step-dad moved into a house in NV that had been inhabited by a clearly crazy women, before they bought it. They were not told prior to the purchase (I think it was either foreclosed on or sold and she was evicted). After they moved in, the crazy lady started showing up demanding that they leave her house, coming to get her mail, tossing theirs, etc. Then she started breaking in. They came home from a vacation once to find all their frozen meat (step-dad's a hunter, so there was a ton), all over the living room and she was in there, in the back bedroom, hiding by the bed with a knife.
This couple have gone to several commitment hearings to beg that this scary woman be locked up long-term. Most of the time she is released after 72 hours. Sometimes she's not committed at all. She had a mother that disappeared once after a drive with her daughter in the desert. Daughter had her purse, IIRC. Mom has never been seen since. And yet this couple are powerless to totally protect themselves from this woman. That's just wrong.