I listened to an interview that he did on National Public Radio. He said that Starbucks doesn't support or oppose gun control but he just asks that people don't bring their firearms into their stores. There are no signs saying guns not allowed, they would just prefer you don't openly carry them. He also said that they will still serve you and not ask you to leave because he doesn't want his employees having to confront someone with a gun (that is intimidating to some people).
I believe this was the right thing for Schultz to say. They are pretty political but he isn't saying don't come with a gun, just that they would prefer if you didn't. That is fair to me because it is a business and they can ask whatever they would like because they have the right to, much like we have the right to possess firearms.
-JF