Discrimination, from a legal standpoint, means discriminating against a person based on that person's identity. If you're willing to do business with the person in question and offer them exactly the same product that you're offering everyone else, you're not discriminating between customers, you're discriminating between different types of products that you're willing or not willing to produce.
When you conflate these two concepts in order to "win" the argument, you're the one being obtuse.
#1 There was never any discussion of design (so saying things about requiring two grooms is false). This is agreed to in court documents in the Statement of Facts. To say different means you think Mr. Phillips (the baker) is a liar.
#2 The bakers (both Masterpiece Cakeshop and Sweetcakes by Melissa) both admit in court documents that the provided the product in question "i.e. wedding cakes".
#3 When you refuse to sell the exact same product based on who the people are, than yea you are discriminating between customers.
Below is one of the wedding cakes in the Masterpiece Cakeshop catalog (
Wedding | MASTERPIECE CAKESHOP). Mr. Phillips would sell the cake to a different-sex couple, but would refuse to sell it to a same-sex couple. Same cake different people, basis then is the customers.