"Why not push to increase their low wages and get some job protection, things that could “make it a sustainable job for everybody?”"
It's obvious they don't know anything about the coffee business. Smaller shops have razor thin margins. Ignoring economics and strong arming the business isn't going to create a sustainable job with better benefits.
In our current economy, most people aren't willing to pay more money for the same cup of coffee.
The result will be what I saw with the dozen or so coffee shop workers that tried to unionize in my area: The businesses all closed and the workers were out of jobs.