because...

the right of a person to swing their arm ends where my nose begins...

everyone should be able to do as they wish, so long as no harm is done to others. Unfortunately, sometimes we can't count on our fellow man to follow that simple practice, so we find ourselves in a position where we have to find a balance between freedom to do whatever we want, and protecting ourselves from those who would do us harm.

everything you do is going to have a consequence, and that's the way it should be. If you dress like a tramp and as a result the neighbor down the hall gives you dirty looks, that's a choice you both make. The neighbor has every right to give you the look, and you have every right to decide that's a price you're willing to pay. But nobody has a right to take something away from you without your permission, be it health, money, property, etc.