@Caution999 made a good point, but let me re-frame it...
Let's say I was a baker. I had a group of Neo-Nazis approach me and ask me to bake a cake with a giant swastika on it so they could celebrate the death of millions of Jews during the Holocaust. I refuse to bake them the cake.
Is that discrimination? Could they take me to court and win? Do you think I would be willing to bake a Neo-Nazi a birthday cake?
You see, this isn't about refusing to serve people because of their race, religion, or sexual preference. It's about refusing to serve people because of what they're celebrating, and the fact you want no part in celebrating it.
Earnestly comparing gay people to nazis. Jesus fucking Christ. ---