I thought Tip is voluntary. And they print the 18% on the bill?
Well, as a European I also think it is a bit much. But maybe here the waiters don't get a lot in hourly wages and they have to live from the Tip.
Still, if it is voluntary, it should be up to the customer how much You want to give.
If it is mandatory, it should be added to the price. See, if the customers still come when the restaurant is so expensive.