In general, though, there's a large disincentive to try to mess with someone who is armed as well. In the one against several case, this really doesn't work. If you just start going violent, anyone else who is armed will simply shoot you. Unless you are in the habit of throwing away a lot of guns, they tend to implicate you in the crime. No rubber gloves or whatnot.
Guns have less anonymity than knives, bats, swords, etc.
The police won't start to look in all the houses for a particular gun. Again, law protecting private property. Therefore anyone with a legitimately purchased gun could not use it for crime without automatically implicating themselves. This also gives the owner a large incentive to make sure that their gun does not fall into someone else's hands. For unregistered guns, it still gives you an incentive to dispose of the gun immediately after the shooting.