The problem with putting people in institutions is that they are rarely 'cured'. In fact, the atmosphere in most of these institutions is likely to reinforce the existing behavior, or even create undesirable new ones.
In general, psychology and sociology are inexact 'sciences' at best, so trying to use their institutions to immunize the entire species to psychotic behavior is unlikely to work. The best we can hope to do now is limit the damage they cause by denying them the tools. Banning weapons is no 'cop-out'. If your only goal was to stop shootings like this, a government could do so by removing the tools, though this would obviously take decades. However, there may be legitimate reasons for not banning weapons which are more important than stopping random mass murders every few years.
In general, psychology and sociology are inexact 'sciences' at best, so trying to use their institutions to immunize the entire species to psychotic behavior is unlikely to work. The best we can hope to do now is limit the damage they cause by denying them the tools. Banning weapons is no 'cop-out'. If your only goal was to stop shootings like this, a government could do so by removing the tools, though this would obviously take decades. However, there may be legitimate reasons for not banning weapons which are more important than stopping random mass murders every few years.