i'll address these one at a time...
1) very few crimes are committed with assault weapons, so why the need to ban them? the last numbers i looked at, assault weapons accounted for about 3% of guns seized by police. so a ban of such weapons will have little to zero impact at addressing violent crime. the virginia tech shooter only needed a glock 19 and a p22, neither of which are assault weapons by the anyone's definition but the victims.
2) that is absolutely not near reality, the criminals would have all the guns they need through black market. just like mexico.
3) dec 11, 2012 clackamas oregon, mall shooter kills two shoppers before his gun jams, while clearing the jam, an armed citizen in the mall drew on the shooter with his pistol. the shooter, just getting his gun reloaded, retreated to a hallway and killed himself.
The first point you still don't give a valid reason as to why Assault weapons should be allowed.
2nd. You still have not said why you think only the government having these weapons and the public not, is bad.
3rd. I am glad to hear that someone armed with a pistol (not not an assault rifle) foiled someones plans to murder people, albeit he didn't kill the gunman but the end result was the same.
my names's Petey and i have gigantic balls