Ever heard of the black market? Also, one other point: a hand grenade is really loud, bright, and kicks up a lot of debris, so people will spot the murderer easier. With a gun, you can buy a silencer, which will make the gun shot almost noticeable. Also, a gun is easier less noticeable. Also, hand grenades are not restricted, but are just strictly regulated. Next, one does not require a hand grenade when they go hunting, and when they are defending their home, that would just be quite ridiculous. The government has made a lot of different drugs illeagal, but people still get them. Have you heard about when the government made alcohol illegal? Well, if you haven't, alcohol usage was at it's highest peak during that period of time. People can bribe politicians, smuggle, and use the black market in order to get stuff that is illegal. Next, criminals WILL NOT OBEY THE LAW! That is quite obvious. So even if America successfully makes guns illegal, criminals will not obey the law. Last, but certainly not least, even if America successfully exterminates the usage of guns throughout the USA, criminals will find other ways to kill. They can use complicated weapons that technically are not illegal, use bombs (if, in this alternate universe, the USA does not successfully exterminate the usage of bombs), knives (which are in almost every American home), chemicals, psychology, their own body, fires, and other such things. They will always find a way to kill. Guns have not been around for all of recorded history, but before that, people killed just as many other people using swords, singing cities,