Clearly not a "physics expert." Nor a reality expert. I suppose if you had a revival meeting inside of a wooden barn in your home state of West Podunk, you might be able to kill a bunch of people with a gallon of gasoline, providing the locals didn't smell it and come out and beat the living crap out of you before cutting off your balls, but a gallon of gasoline in a modern building with proper fire exits could very well not kill anyone. Whereas emptying a 100-round clip into a classroom full of 6-year-olds is pretty certain to kill most of them.
And keep in mind that there's nothing macho or ballsy about starting a fire with a gallon of gasoline. I don't recall any video games where you go around starting gratuitous fires. Whereas there are a butt load of games that glorify some macho pinhead going around shooting people.
And of course I could also point out that your little gasoline scenario is pretty much hypothetical in that no one has recently set a pre-school on fire. Again, perhaps, because matches don't make much of a penus substitute for those closeted individuals who feel unmanly.
The sad thing is, the guys running Slashdot haven't figured out that they've been hijacked by a bunch of NRA plants. At least they should be proud that the crazies expend more effort distorting the facts here than they do over at Wikipedia, which is sometimes referred to as Wikiganda by the cognoscenti. And by the way, just to keep this discussion honest, here's the ENTIRE 2nd Amendment, including that mysterious bit about a well regulated militia:
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."