In the absense of legislation madating Cho's name be on the prohibited persons list, Cho was able to engage in the legitimate firearms market. Cho had been adjudicated a danger to self after being arrested for stalking female strangers. The State of VA decided not to voluntarily forward that info to the NICS dbase, as per fed request. This law says all states must forward that kind of info.
Legislation like this feeds into the culture of Fear the liberals have been building up around the issue of self defense. It isn't needed and does a LOT more harm than good. Never give your potential enemies a sharp stick they will eventually use to poke you with.
Cho was not adjudicated to be a sufficient danger to justify denying his freedom? If so, he should have been locked up. If not, then he was a free person.
If judges are given the authority to disarm people without locking them up, you can bet that many of them will do so with even the tiniest sliver of vague justification. I see no good reason to give judges that option.
If the Second Amendment doesn't protect the right of all free persons, who does it really protect? One may reasonably quibble about which people should be 'free' or 'not free', but one shouldn't lose sight of what disarmament means.