If you spend enough time in the United States (either visiting or living here), it is reasonable to expect you to know that the staff who provide sit-down and bar services are living off their tips. Knowing this, you also know that any position you adopt is nothing more than rationalizing taking food out of a perfect stranger's mouth. To allow someone to serve you, knowing that the custom is that you compensate them for good service, and then walk off without leaving just compensation is theft.
That said, my understanding is that waitstaff in Europe are paid an actual wage, do not expect tips, and (gasp!) do their job anyway.
I would much prefer that waitstaff made a reasonable wage and considered tips both a nice surprise and a sign that the customer was supremely satisfied. It'd be sort of like taking the manager aside to sing their praises, only they get a little bonus instead.