I hope you do not actaully think that is way things are or the law works because it does not.

In the US the law allows for you to make the case of self defense, it is a defense for violations of the law. I.E. it is always illegal to kill someone, but it is a defense if you kill someone who was trying to kill you..

Things like bobby traps, or poisoning your food against a thief would not be legal under American law. For example I can not setup a series of Automated Gun Turrents in my home to kill anyone that breaks in, but I could (in some states) shoot someone myself if they break in.

In a food theft case as an individual could in fact assault someone possibly even commit battery against someone in order to prevent the from stealing my lunch but I could not say put bobby trap that could cause physical harm to them on the lunch