I just want to add that I don't think gun ownership should be a constitutional right. But it is, and until that changes, you can't take rights away from normal people who have committed no crime.
Well, actually.
You could theoretically read the 2nd amendment in such a way that it is intended for militia purposes, and various interpretations over the years from courts have also included self defense in that definition. And you could further read an implicit connotation that the right to harm other people outside of defense is not protected. Further, it is already constitutional to take rights away from people who are potentially harmful to others. So using that as a basis, you could say that people who could very potentially harm other people lose their right to self defense because they are not of a right mind. But that's tricky.
And further, you would have to bring people to court and provide evidence of all of this because there is a 5th amendment. So, this is... Uh... Hard.
Something that might work is a ban on weapon purchases by anyone convicted of violent crimes. That's not unreasonable and has precedent. And it would have stopped Omar, because he beat the living shit out of his ex-wife.
