The minimum law doesn't apply to waitresses,waiters or barmaid, at least in my state. Heck at pizza hut here they only pay like 3 or 4 bucks an hour to waits because they are tipped employees. And I know several bar server/waitresses who only make a little over 3 bucks an hour. These type of employees are dependent on tips, so it's only right that someone who waits and serves my needs gets paid accordingly. If they are good they get a nice tip if not I leave a few pennies then they know they need to improve. And if it is really bad I leave a complaint with their boss.
To each their own, but if someone is going to physically take care of my needs and provide me with a pleasant experience I show my appreciation.
The only ones I have an issue with are like pizza delivery, they make minimum and then the pizza restaurant adds a delivery cost to your bill then the driver expects a tip when they are getting 2-3 bucks per delivery from the store they work for on top of their minimum wage.