If you look around in society, there are some people that have little value for lives of others. Life cannot be that bad to where you have to murder innocent people because of your drama you have in your life. Honest people have a right to live.
"Do Not Murder" is Way to Happiness precept #8. There is a big difference between the two words "Kill" and "Murder". A law against killing would rule out all self defense. If you had a mad person shooting or harming people at random and you had the chance to end it, The RIGHT thing to do would be to shoot or harm that person even at the risk of killing them.
"Murder" is another thing entirely. The definition of murder is, "The unlawful killing of one (or more) human being by another, especially with malice aforethought". Some people have gotten away with murder by saying they were insane. It stands to reason that anyone who would solve their problems (real or imagined) by murdering another is insane. That is a solution done by the stupid and the evil. Communication is a far more effective weapon and solution than murder.