So I see there's apparently now a campaign to boycott Starbucks because of this. The social media blunt instrument strikes again.
I'm not sure what Starbucks, as a corporation, could have done differently after the fact. They apologised for what the employee did, and apparently are taking disciplinary action. What else are they supposed to do? Starbucks actually has a reputations as a fairly progressive company.
As far as the police go, there's not much differently they could have done. Starbucks is a private business, and a Starbucks cafe is private property. If they ask you to leave, you leave. If you don't leave, you're trespassing. Once the police showed up, they again apparently asked these guys to leave, they refused, and at this point the cops had little choice but to make an arrest.
What this employee did in calling the cops on a couple guys who were doing nothing but sitting there talking, was of course, wrong. I don't know about this particular Starbucks, but in every one I've ever been in there are always people hanging out using the wifi without ordering. So if these guys were specifically targeted for their race, that's a problem. But until I see evidence that this is some kind of problem nationwide with Starbucks (and get more facts as to what happened in this particular instance), I think the calls for boycotts are a bit premature.