I listed 14 crimes committed with AR-15s in the past two weeks that resulted in dozens of injuries and several deaths, including one child and two police officers. I probably missed several more when doing my search. The easy access of AR-15s and other assault style weapons along with high-capacity magazines is definitely a problem in the United States.
Every life is important. If banning AR-15s and high-capacity magazines saves just one, it's worth it. In reality though, it would save many. The thing is, the same people that want to see a ban on assault style weapons and high capacity magazines also want other gun control reform including things like universal background checks on all gun purchases and transfers, including private transfers and sales at gun shows; requiring a multi-day waiting period on all gun purchases, requiring registration and a license for each gun that a person owns, having a minimum age limit of 21 to purchase a handgun and require a hunting license for purchases of rifles or shotguns by adults under 21 who are not in the military or law enforcement; and require training and a proficiency test for the type of gun being purchased. All of these policies need to be enacted, not just a ban on AR-15s and similar assault style weapons and high capacity magazines.