a christian baker has the right to not bake a cake for a gay wedding, he's an asshole for not doing to, but he should have the option to do business with whomever he wants
a gay barista is also more than welcome to kick out anyone he wants, and if he does it based purely on their religion he's also an asshole, but it's his choice to do so.
however, if he in fact kicked them out for distributing anti abortion literature, then it's totally different from the cake guy.
one's prejudice the other's just a reaction to an action
unless of course the soon to be married gay couple was also handing out literature agressively trying to turn people gay.