Foundation for law

Hello. I was thinking this morning as I rode the bus on Western jurisprudence and in specific the contradiction with illegal marijuana and legal alcohol. That is NOT what I wish to discuss. Imagine, if you will, you and 1000 people are stranded on a deserted planet and must form a society. How would you decide what is and isn't legal, or what should and shouldn't be legal. Please, if you can, avoid mindless thinking like "x is bad because it's wrong". Think less along the lines or your social conditioning and more along the lines of what is the purpose behind your legal system.

I will go first. One fundamental rule should be that laws should be designed to punish those who hurt others.