Actually, I think the argument is should the state have the right to prevent risk. If someone is not of their right mind using drugs and is at risk for such violent behavior, does the state have the right to prohibit the substance that causes the behavior?
Drug users cannot say that they have the right to the drugs, but no responsibility for the behavior resulting from them. The old, "I was on drugs and didn't know what I was doing.", is no defense from prosecution.