The tyrants in power would have faced a guerrilla war. Maybe that is why our forefathers added the Second Amendment to the United States Constitution. They wrote the Constitution with the preservation of liberty in mind. Life sentences for 10 year old kids who murder people will not stop killing. Similarly, denying citizens the right to associate with whomever they please will not stop street gangs or crime.
Crime is already illegal.
Teen killers and gang membership are products of long-overlooked social problems like parents who don't parent and schools that don't discipline. Tough laws have not stopped crime. Tough rhetoric about crime and draconian new laws do manage to get politicians elected or reelected. It may come as a surprise to legislators, but the public defender's clients don't keep up with new developments in criminal law. Even lawyers and judges find it necessary to refer to textbooks when they need to know the exact penalties that new criminal statutes provide.