American here. I know it's hip and trendy to bash on Starbucks, and it's not entirely undeserved, but I go to my local Starbies on the regular and find the quality to be just fine. Black drip coffee has improved dramatically. It's not sludge anymore.
Secondly, I occasionally visit a 7-11 near my home that has robot coffee drink makers and I have found that for less than half what I pay at Starbies for a fancy drink I get a good coffee drink. I could see a half-dozen of those robots pumping out fancy drinks that rival handmade ones, especially at a lower price point.
Finally, unionizing Starbucks would only lead to decreased quality and higher prices. Besides who want to work as a barista as a career?