Additionally suppose what was at issue was a slogan printed on every wedding photograph which was clearly discriminatory because it was also political. Something like, "One man. One woman. One holy marriage."

If a photographer does this, you must choose between political speech and non-discrimination because the political speech interferes with a right of a vulnerable group to enjoy their purchased goods. Otherwise where do you draw the line?

Or what do you do if a cake decorator insists on a similar slogan on the wedding cake and opposite-sex decorations? Surely this is both political speech and functional discrimination, right?

The EFF avoids this by having a narrower focus.