it's sad and true on the matter of security, but even then, how plausible are security measures? after these incidents there is always a big tightening of the belt, a wakeup call and many places smack down on security.... but at the same time, is it plausible? probably not. to effectively secure the building they'd have to reduce the number of entrances, guarding all doors at all times the building is open. they'd have to pay these armed guards and they would probably have to pat down every entering student. once we clear through the harassment suits to follow (yes, they ALWAYS show up in security with a pat-down that has any hopes of finding a concealed weapon) and the general blow to morale... people being late more often... and NOBODY wanting to pay more money(after all, university/college/other post-secondary education already costs an arm and a leg for people just getting by) that these measures will cost the school. and even after all that.... if someone is going to commit mass pre-meditated murder, they're more likely than not going to have a plan for security. also, those lines generated by being filtered slowly through doors? probably an even better target.
There is no viable answer really, not that will go anywhere or do anything other than lull you into a false sense of security.