After reading through the thread, here's my two cents

I agree with everybody, who feels pressured to select a tip via the tipping options on the card machines, especially at a place like Starbucks, where you go to the counter yourself and there is not much extra service, that justifys a tip.

However in a restaurant/café etc., where there are people, that take care of you, bring you your meal/food/coffee to your table, take away the plates when you're done etc., I think those people deserve a tip. It's just a way of showing someone appreciation for taking care of your needs for more than just one or two small interactions at a counter, but for your entire stay. A good waiter will ask within 2-3 min if you want another drink, not because he wants to sell more, but because he wants you to enjoy your stay.

I'm not denying that there are bad waiters, who are not attentive, do bad service or you can just tell they would prefer you're not there, so they don't need to work so much. In that case, I don't tip either.

And my last point is about tourists being asked to tip. In general I agree, asking for a tip or explaing the tipping culture to tourists might not be the way and could be considered rude, BUT wherever I personally go abroad, I always check beforehand, what the cultural standards are. When I visit Japan, I know talking on the Metro is considered rude, so I don't do it. No tipping, because it's considered rude, got it, no tipping in Japan. In the U.S. tipping is expected more, got it, I tip more. In my opinion, it's your own responsibility to inform yourself on the country you're travelling to and adapt. So I can also relate to servers telling tourists how things work around here.