One might argue that the lesbian wedding case is more like the interracial wedding case because both involve moral disapproval, as opposed to mere dislike. But if anything, that weakens the case for legal interference: We generally weigh conscience more heavily than mere discomfort when assessing people’s liberty interests. Besides, those wishing to punish me in that case surely wouldn’t be appeased if I had said: “Look, I have no moral problem with homosexuality; I just think it’s weird and icky. Like clowns.”
Nor can one assimilate the lesbian wedding case to the interracial wedding case, and distinguish it from the birthday party case, by a “born this way” argument. Put aside debates about the etiology of sexual orientation or the social constructedness of race. Clearly, age is entirely a function of when one was born, and thus outside voluntary control. In other words, the birthday party case hinges on an involuntary characteristic just as much as the interracial wedding case does. So that won’t help.
Maybe the difference is that the wedding cases both touch deeply on issues of identity in ways that the birthday party case does not. That answer seems partly right. But surely children’s “childness” is a significant part of their identity, too, just like my middle-agedness.