I just read the Second Amendment againt and I don't see anything that limits the right to possess a firearm to law-abiding, mentally stable people. While that might be advisable in modern society, the mechanism for achieving that goal is not through legislation, but through a Constitutional amendment.
I really don't care if criminals have guns...if they want them they already can get them...but I do care if they use them criminally. There's a huge difference between possession and criminal use.
If a person cannot be trusted to possess a weapon then perhaps they shouldn't be trusted to be free or unsupervised.
None of our rights are absolute. The government does have the assigned duty of protecting the citizens. Any act to protect citizens will, in some way, limit the rights of citizens.
The question isn’t therefore whether it is proper for the federal government to have any restrictions at all on gun ownership. Just like with free speech rights, there are valid limitations based on the rights of each person to life and liberty.
I still don’t know if Cho was known to be mentally ill sufficient to trigger valid government action against his right to have a weapon. He certainly SEEMS to have been, but I wonder how “serious” this stuff really was at the time, compared to how it is judged now that people know the end result. It’s easy to look back and remember things more harshly.
I would note that nothing in the constitution explicitly states that a felon can be denied his right to free speech or to own a gun, but few would argue that convicts should have CCW privileges.