In the USA, plenty of counter-service restaurants/shops have tip jars. Further, many counter-service food outlets have added a tipping option to their credit card process, usually with 15% as the minimum.
Starbucks could, at any moment, bar individual stores from placing a tip jar at their registers. Just like McDonald's. No tips, no issue, no should I or shouldn't I?
If you're going to be outraged that Starbucks offers you the opportunity to tip people at the counter, perhaps I should feign outrage that you spend your money on starbucks instead of making your own coffee and giving the difference to the homeless. Starbucks has a significant profit margin after all; that is money you could be donating!
I'm pretty damn skeptical of that, since in America the vast majority of customers do not put anything in counter tip jars. Maybe you've got some sort of strange selection bias going on...
I see this as just a little bit underhanded... creating the expectation of a tip in situations where one is not needed.
Also, the presence of a tip jar does not create the need for a tip.
Most people run tabs on plastic nowadays, so how's the bartender supposed to even know what they are earning per drink? I prefer to pay in cash & tip dollars as I go, & i find most bartenders are more than happy to get them & continue good service when they see paper coming their way on every transaction.
Nothing like trying to help income inequality than to promote progressive income tax evasion.