@21 - I think freedom of association certainly applies if we're talking about churches, non-profit groups, and other organizations whose concerns are less material. I actually believe that churches are corporations are governments; they're all just different ways that this particular primate species organizes itself. But where ideological, spiritual, or aesthetic differences remain "practical abstractions" by which we can maintain tribal identities (which nation-states will never satisfactorily replace), all modes of organization which directly impact material possession, availability, or exchange (government, corporation) need to be held to similar and more universal standards. The material--not merely psychological, at least in enough cases, I'd wager, to be statistically significant--inconvenience of being refused service is problematic.
The evangelical florist may be compromising a deeply held conviction by making and arrangement for a same-sex wedding, but only in the same way and same degree that an evangelical Best Buy employee would be in selling a TV to someone who's going to watch porn on it. Neither threatens the employee or business owner's right to associate as they please on ideological grounds (they can invite, or not invite, whomever they care to over for dinner; they can continue to go to the church[es] of their respective choice, and so on). It simply says that your right to free association--i.e., the right to ideologically
discriminate as they see fit--avoid placing material consequences on the shoulders of the segment of the population with whom they disagree.
...the state demanded that you accept something you consider immoral, perhaps you're an animal rights activist that is forced to harm an animal or some such thing,
Not really an apt comparison. A more accurate one would be to suggest that the state would still demand that an animal rights advocate serve someone who harms animals outside the scope of the business transaction. After all, the florist is not being asked to do something outside the scope of either her actions or her morality; she's simply being asked to do what she does for a customer who can pay.