He said he would not make a custom cake for a gay wedding but he will make a custom cake for a heterosexual wedding. 
It does not matter if he has served them before.
If a man comes in my shop and I do not murder him, that does not guarantee I will not murder him in the future.

What is the point? Wow.

What if your wife was dying and needed emergency medical treatment and a doctor told you that he can not give treatment to a woman due to his religious beliefs? No big deal, just go find another doctor, right?

Would it bother you if the baker refused to serve white people?
That is what he is asking the court to allow.
He wants to be able to legally discriminate based on his religion. 
If true, I can argue that it is legal for me to sell my foreign neighbor into slavery. The bible says it is okay.