Starbucks may like gay marriage, but it also, via a subsidiary, likes exploiting prison labor. Sure sign of the diff between a latte-sipping, Volvo-driving, Meyer-lemon squeezing neoliberal vs. real liberals is this. In this particular case, I don't think Starbucks is that bad toward its own direct employees, but that's not the full picture.
It's one of a number of U.S. companies that exploit prison labor operations. And, while we normally associate this with private prisons, government-owned prisons in some states also have prison labor operations.
Maybe that's because the federal government has been in this business for 80 years. Their home page is sickening, looking more business-slick than many actual businesses. Wikipedia has its history. And good old ALEC pushed regulation allowing prison industries much more latitude in competing with free world workers.
I, too, support gay marriage. But, I don't use that as a cover for letting businesses continue to exploit prison labor in what violates at least the spirit of the 13th Amendment.