I am not a fan of pink firearms, nor of Hello Kitty rifles, yet those have brought new shooters into the fold, so I am hardly going to discontinue doing business with a store because it stocks them. It would be counter-productive.
For every disaffected loner killer you want to name, I could probably find a charismatic Ted Bundy or Charles Manson. You are buying into stereotypes too much.
If I stopped doing business with every store that carries something that I find ridiculous, I would have a very hard time shopping. For instance, I would have to stop going to gun shops that stock various iterations of the Judge... And, stupid though I find them, the Judge variants have attracted a bunch of new shooters.
Again, if Deagle shooting gamerboiz offend you, then take one or two under your wing and educate them. Your current approach is, in my opinion, self-defeating.