There is no "participation" in events by vendors. The African American baker is a baker, not a participant. The Gay florists is a florist, not a participant.
Applying the condition of participation broadens the mandate for vendors into and area that is untenable. Wedding vendors are not participants, yet invited guests are. Wedding vendors are not participants, yet clergy is. Wedding vendors are not participants, yet family is.
Vendors provide services, they are not participants.
Hmm... Now as a vendor, does one or does one not provide the means to celebrate deviancy; where the wedding is one which seeks to join one male with one male, which as you may have heard, represents a 180 degree deviation from the human physiological standard.
"Deviancy" is in the shallow heart of the individual. If you are a baker, your mandate is to bake, decorate and deliver a cake. Not to make any judgement about the event. You, as a baker, are not required to supply any form of approval or disapproval of the event. Such judgments exceed the mandate of baking, decorating and delivering a cake.
Events like Gay weddings do not hinge upon the moral code of the vendors. The day after the wedding, those vendors are preparing for their next client. The vendors do not haunt a wedded couple to make sure that the couple's activities meet whatever code of comportment the vendor has. Likewise, the wedded couple does not interfere in the personal life of the vendors.
By what authority does a wedding vendor decide which marriages are acceptable and which are not?