Simon speaks sense.
As JWs we were, at one time, willing to not salute the flag, sing the national anthem and sign a birthday card because our conscience would be violated. Some governments who had a national draft provided alternative service for those who would not take up arms against their fellowman.
If a gay couple walks into a bakery they can buy any cake they want.
If a gay couple walks into a bakery and asks the baker to decorate a cake with a gay themed wedding then this would violate the baker's conscience.
The baker has options:
# 1 He can ask an assistant (if he/she has one) to do the artistic expression or
#2 He can sell the pre-made cake as it is and ask the gay couple to find an artist to decorate the cake.
#3 If said wedding cake does not exist, he could meet them half way, make the cake with the marzipan and the icing according to the gay couple's specifications and ask them to finish their decoration. The baker gets paid and the couple get their cake.
#4 The gay couple can find another baker knowing they can still get their cake (and eat it too).
The JWs here might consider this case a "conscience matter"