I stated in another thread my for a similar question. Prohibition tends to work only for those who are inclined to accede to the law. History has shown that in the case of a prohibited activity, object or concept that the law or prohibition does not remove the alleged danger from society. The prohibition on liquor was a prime example. The prohibition on so called "recreational drugs" is another.
As to the prohibition on guns, I think the following describes how well it really works. Columbine, Virginia Tech and Aurora there are more but I'm keeping the list short. All were by law, gun controlled. In those cases only those inclined to follow laws were doing so. In those cases the individual(s) who were not inclined to follow that law as well as the laws prohibiting murder, assault and mayhem were not dissuaded. In those cases they were not stopped until someone with the means to end the situation responded and started to take action.