Aurora shootings.

[tempest]

ban guns? for what reason? the tool is not to blame, the person and the society he's from is, as well as his natural state.

You're right, but you don't have to make it easier for them.

just because someone could kill with a rubber fish doesn't mean they should be outlawed for that reason.

Right again, and a chainsaw or an axe or even a plain old kitchen knife would have been much better examples. I have two objections, though:
1) With none of those things you can trivially kill a dozen people in 60 seconds. On the other hand, that's no problem with an AR-15 and a 30-round magazine.

2) There are many legitimate reasons for having an axe at home. Tell me one good reason why a civilian would need an assault rifle. They're not really useful (and banned, I think) for hunting, they're a constant danger unless properly secured (kids, burglars, etc) and so on.
And don't even get me started about the idiotic "I need to defend myself" argument. AFAIK more people are erroneously shot by civilians because they're mistaken for criminals, than actual criminals. Does "Trayvon Martin" ring a bell here?

Also, you might want to compare the homicide rates of various (western) european countries with strict gun laws to that of the US, as well as the percentage of homicides involving firearms.