No one is stronger on the 2nd amendment than I am; my wife and I collect vintage firearms. But in my experience your theory doesn't actually hold up. The psychos that I have had to deal with over the years do not generally think about the consequences of their actions. A naked psycho with a hand gun once pulled the trigger several times while it was pointed at me at close range. It was by the grace of God that he had loaded his magazine wrong and that I am still around to talk about it. He intended to commit suicide and hoped to take someone with him.
Like I said. When they went on a rampage 1 MAYBE 2 at most would die before they were put down.
If everyone had a gun it would be a whole hell of a lot better then what we have now.
Any infringement is against the second amendment and thus against the constitution of the USA. Therefore it stands to reason; anyone should be able to purchase a gun. If you say “well sooooooooooommmmmmeeee people shouldn’t”, you cannot go on to say in the next sentence you support the second amendment. Period.