If that German student, Hamilton and Ryan had not been able to get firearms so easily then those masacres would not have occurred. The fact that Ryan was able to buy a fully automatic weapon is ridiculous. Don't you realise that by making it so easy to get firearms you are guaranteeing trouble?
As for that German, he was hardly a hardened criminal, the man only had a speeding ticket! What he did may have been a spur of the moment thing, he hadn't owned a firearms license for long. If he hadn't had a shot gun and a pistol I doubt he would have killed anyone.
Making home made explosives or a gas bomb that can kill large numbers of people is a lot harder than shooting people. Ammonia chloride is an expectorant. I think you will find its ammonia mixed with sodium hypochlorite (the active agent in bleach) produces chlorine gas. Besides, banning cars and bleach etc is hardly the same as banning firearms, since guns can be used to kill far more easily and effectively.