Isn't it pretty standard practise to not allow this kind of thing? Brings to mind the Palestinian protests made at eurovision, that resulted in punishment. A hearthstone tournament just isn't the place for it.
Really the only reason people are latching onto this ban is because it's a message they agree with, if it wasn't then they wouldn't care. But political statements being ok to make or not shouldn't be dictated by whether it's a popular message or not.