All they did was to essentially ask politely not to be the focus of our social events.
This is the directly quoted line from the letter issued by the CEO of Starbucks:
For these reasons, today we are respectfully requesting that customers no longer bring firearms into our stores or outdoor seating areas—even in states where “open carry” is permitted—unless they are authorized law enforcement personnel.
It is not an outright ban (not that they have the authority to do so anyway, with any weight of law), and not a policy completely prohibiting the carry of guns.
It is however, a request not to open carry any guns at S-bucks. Much more than simply "please don't hold protests here." I have carried concealed numerous times at Starbucks since that letter was issued.