Having a debate about tips is (from my experience) usually getting very hot if US is amongst themselves.
Add some euros to the discussion and it's not moving anywhere.
US and EU is completely different, there's no purpose at all in comparing.
From what I understand, in the US, waiters need the tip to survive. And the tip isn't really a tip, it's a more or less fixed percentage that you can't decide yourself. I've also heard that restaurants will not let you leave if you do not pay a tip. Literally stop you from walking out if you don't pay a tip. It's basically a tax on food, just without a legal background, just a social one.
In (most places in) the EU, the waiters get a shitty wage as well, but enough to make a living. When you don't give a tip, most waiters will ignore it, some will be slightly weird, but rarely does one say something.
In the end, I think the cost is the same in both EU and US (relatively speaking).
As for my personal tipping: I tip usually around 1€, for guys that deliver food to my flat, for my favorite diners where they serve exceptionally good food, and when going out and the service was at least ok. If I feel the waiter didn't really care, I don't tip.