Do guns remove one's ability to think reasonably?

I've heard many reasons why people are afraid of guns but one central argument seems to imply that guns aid impulsive behavior. If a person is depressed and has a gun they're more likely to kill themselves than if less immediate options were only available, if a man gets into an argument he's more likely to commit murder even if he would never have done so without a firearm, etc. My question is what is it about guns that makes people assume that others can't control themselves or think rationally around them? If I'm angry and in a car I doubt anyone would fear me impulsively running over a crowd of people. If I get into an argument in a steakhouse people don't fear me jamming a steak knife into someone's neck. The vast majority of people who own guns take them very seriously and those who don't see them in a very serious light, and yet so many of us feel that when we're around them we can't help but kill each other. Why is this such a common assumption?