If you were shot by a lone gunman it doesn't mean you did something wrong. Anybody who posses the gun can shoot anybody or anything according to the person who sell it. Ability doesn't mean it's a Right. If we walk this path we could simply be flagging each other in a flagging war which would be extremely counter productive.

A gun is designed to be able to shoot and kill. But only in certain circumstances the firing of a gun is justified.