Liberal babies and pansies would scream. 
there USED to be police on most campuses.  Then there were budget cuts.  And police get cut before the "admin assistants" making $65k a year to carry a clipboard and "help out" in various classrooms.
I'm all for a common sense solution.   
Some people are right - there are too many guns, too easy to get, too little training required, and too little punishment for those who break the law.  Most people don't need a 30 round rifle - it should be available BUT should be harder to get than just signing a paper.
On the other hand - this kid was 20 and was illegally carrying a gun to the crime - he didn't give a shit about the law.  More laws wouldn't have stopped anyone here.  
Greater security should be the solution at the school.  They had a great security system that he had to SHOOT through - the intercom put the shooting noises for the entire school to hear - IF the doors had locks, the teachers would all lock the doors and cover windows (they do practice this) and that'd minimize his impact.  BUT the #1 solution would be a cop on every campus.  Small cost for a highly trained, vest-wearing cop who is very familiar with who belongs and who doesn't.