I do understand what discrimination is, you just don't understand what it is not.  The baker offered to sell the couple any cake in the store, but he would not create a personal work of art endorsing a particular event.  He says his reasons were religious... I say it doesn't matter.  If he says, "You are welcome to buy anything in the store, but I'm not creating a personalized custom product for this event," that's not discrimination.  It is not a fact that the baker discriminated... it is, I grant you, a debatable matter of opinion.  The Supreme Court will Support one view or the other, and then it will be law.  That doesn't make it right or wrong... it just makes it the law, and there will be people who disagree with it either way.