Let's use this analogy:

There is a baker who is a Black Orthodox Jew. Three customers (a Neo-Nazi, a KKK, and a gay person) come in, separately, and they select items he has for sale and he rings up their individual purchases. 
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Is there any form of discrimination there? No.
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The next day, those same three customers return, separately, and they each ask the Black Jewish baker to decorate a cake they want to buy. The Neo-Nazi wants a cake decorated with swastikas and a picture of Hitler; the KKK wants the cake decorated showing a man being lynched; the gay person wants a same-sex wedding cake. He respectfully declines all three requests.
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Is there any form of discrimination there, and if so, exactly what is being discriminated against?
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"Yes," there might to some sort of "discrimination"....but what is being "discriminated" is the "artwork" he is being asked to create with his artistic talents.
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He cannot discriminate against "people," but "offensive artwork" is not "people."