http://m.npr.org/news/World/126395129 3 separate incidents, all with as many or more victims than some of the biggest mass shootings in the US, and all within a very tight time frame. In each case had there been an armed adult on the campus (in china I realize this will always be impossible without a military/police presence) the likelihood of one of these degenerates getting close to even one of the kids would have fallen drastically, if for no other reason than you don't generally take a knife to a gunfight even if you're crazy.
I generally have stopped talking about my political views and opinions, mostly because everyone I know is of one seriously determined political philosophy or another.
At the end of the day it all comes down to this: do you believe you have the right to do what you need to do to live, and do you believe those you put in charge/care of your children should be empowered to defend them as you would. From a purely biological standpoint, a failure to say yes to either statement means you effectively are a failure at evolution, since the end of your genetic line is the end of you.
From a more moral standpoint, while folks mourn those who die passively, there is rarely any great goodness from the loss of those folks. The killing of a would be assassin eliminates their ability to claim future victims which ultimately does serve the greater moral good.
I just needed to get this off my chest, because I've met so many folks who say 'no guns means no violence' when confronted with the fact that being able to protect yourself means you do get to live, seems to just cause them to glaze over and repeat their mantra as if it has some magical totemic power to preserve their life.