I don't think that need is based on "emotions" as you say. What I'm trying to do here is look at a weapon, see what it brings to the table, and then imagine what a person could possibly use it for (besides shooting it at a paper target, or into the air).
That, you might say, is a dangerous form of reasoning as well, but I think it's instructive.
Take the Soviet
ZU-23, a light anti-tank and anti-aircraft weapon that fires a 23 mm round. Civilians shouldn't be allowed to have a ZU-23. Civilians don't NEED a gun that can shoot down airplanes and blow up armored personnel carriers.
Like I said: there IS a line. I recognize that people can theoretically own full-auto M-60s if they get the right permits. I think that the .50 cal sniper rifles should be in this category. For a need argument, the average person doesn't need a military anti-materiel rifle that can fire armor piercing and explosive ammunition accurately at ranges greater than 1000 meters.