[the author] concludes that, because being a Starbucks barista is so simple and turnover at the job is so high, this might not be a job where a union makes sense. "You can't unionize [cheap service jobs] if nobody wants to keep them," he says.

But doesn't Clark have this backward? Unions don't exist just to help people keep desirable jobs; they exist to make jobs more desirable. It may be true, as Clark says, that being a Starbucks barista will never be hugely fulfilling. But the gig could certainly pay more—when it comes to baristas, there's no complicated global market to negotiate; Starbucks could just write bigger numbers on its payroll checks.

[emphasis mine]

Do read the review, the Starbucks story isn't as boring as you might think.