No. You cannot open business to the public and then have a list of disclaimers based on the type of people you will or will not serve. Gay, straight, christian, muslims, etc. It doesn't matter.

If your religion requires you to discriminate then you should not open businesses to the public. 

As I pointed out to Bill: what's stopping the church of satan from denying services to christian events? You might laugh because the church of satan isn't as large as Christianity but imagine reading a news article where a coffee shop run by a satanist denied a church a large catering order. You'd think "that's discrimination! You can't open a business and not serve certain kinds of people! What an idiot!"

The reason people are for this precedence of discrimination is only because they agree with the baker. They're blind to the underlying issue.