When I go to a Starbucks (or any coffeehouse), I generally order what the person in front of me orders. Again, I don't have the skills and knowledge to order a cup of coffee.
The world has just gotten so complicated. I think coffee used to be "regular" or "decaf". Now not so simple.
Anyway, when I am paying for my coffee, I notice a tip jar. Barista's seem to expect tips. This confuses me.
When I am at a restaurant, I understand tipping. The server provides a service, the restaurant pays part of his/her wages, and restaurant patrons make up the difference. I get it. Pay for performance and all.
I go to the mall and order an Orange Julius, the person prepares the drink and I pay the exact amount. No tip requested or necessary.
I go to the mall and order a fancy cookie, the person selects and hands me the cookie and I pay the exact amount. No tip requested or necessary.
I go to the mall and order a coffee, the person pours or prepares the coffee and I pay the exact amount. And I see the tip jar; the barista expects a tip.
I like patterns in my life, and tipping of baristas doesn't seem to fit my pattern.
Now, I don't know if baristas deserve tips or should have tips, but here is a common-sense approach to the problem.
If I visit a barista every day, I am tipping that barista (considering he/she knows my coffee wants/needs). And here is why: I don't know exactly how I would most like my coffee, but I am fairly sure that I would most like my coffee without saliva in it. If you go to someone often and there is a tipping situation, it makes sense to tip. You will more likely be rewarded for tipping well and punished for tipping poorly.
If you visit a barista only once or very infrequently, tip if it makes you feel guilty, and don't tip if it doesn't (and you are opposed to tipping for the barista). Me, I feel guilty and it is better for me to tip, because the dollar infrequently makes me feel happier. But if you take some philosophical stance against it, perhaps you just like patterns. See above.