Open your own coffee shop. Your business, your call. You want to deal with protests by anti-gun folks, God bless you. You want to risk driving away customers who (for better or worse) are nervous around guns, that's what being an entrepreneurial risk taker is all about.
Heck, you could even make your employees carry rifles. Just show a little class and make sure they're Garands. Because then your M1s will do your (political) talking for you.
You take the risk, you decide. Starbucks is taking the risk in their stores, so I don't see what the problem is with them deciding.