You say that you don't have to tip and then advocate tipping 5-10% for bad performance in the same paragraph? Of course there is no legal obligation to tip, sin

You say that you don't have to tip and then advocate tipping 5-10% for bad performance in the same paragraph? Of course there is no legal obligation to tip, since if there was it couldn't be called a tip-- it would just be itemized billing. But the fact that in the US wait staff can be legally paid less than the minimum wage (before tips) provides an ethical argument for tipping, if not a legal one.