Again, I propose the challenge: Name one good reason why armymen or SWAT team members should automatically be granted more trust with a gun than your neighbors.
Errrrrrrrr
Training and stuff? Having an actual need for them?
If you don't think that defending one's self constitutes a need, then by extension one shouldn't need police, armymen, or SWAT teams to defend one's self, either. I doubt you would be in favor of that.
Training is a fair point (compared to areas where someone can lawfully obtain a gun without training) but can arguably be offset by the context in which they are trained. The nature of the jobs of military and police is one where violence is anticipated. This is why you see, for example, police officers approach a routine traffic stop with their hands on their holsters. The psychological expectation of violence contributes to a greater likelihood that they will be more "trigger-happy" (didn't mean that euphemistically, but for lack of a better term) and make a careless mistake themselves.
We both have surely heard of all the deaths of unarmed citizens by police and otherwise. Highlighting this point, do you think that the recent incident where an unarmed man flagged down police was shot and killed would have ended the same way if the man had flagged down a civilian? Nope. Furthermore, society often approves the use of deadly force by police in situations where a criminal has a knife, bat, or other handheld weapon. Why? Because the police officer was defending himself. By extension of that logic, it should be approved that any man can defend himself against similar threats with a gun.
Edit: On 2nd thought, even "training" isn't a very good reason at all. The reason is that the only significantly important training is that which is relevant
after a threat has been identified. Mental illness not withstanding, basically any idiot will have a good idea when a significant threat exists such that the use of a gun becomes justifiable. Unless you have some paranoia yourself, you shouldn't have much worry about your gun-toting neighbors just lighting up the neighborhood willy-nilly. The question is instead whether you can trust them with a gun after they have identified a legitimate threat to the safety of their selves or someone else. In a home invasion, this won't be much of any concern because the threat is isolated to that environment. And if everyone of sane mind has a gun, the chances decreases that a legitimate threat will exist in a public space (because a criminal knows he has no chance unless he's already committed himself to going out with guns blazing). People don't take guns and start shooting randomly while spinning in circles.