While I understand the premise, I also have to concede that a florist or a baker is not the Church, nor do they hold any position within the Church to decide what is and what isn’t a valid marriage. I do understand that they are trying to avoid cooperating in sin and that is the basis for the refusal. However, what about other customers whose marriage appears invalid? To avoid cooperating with sin, should they also turn away divorced couples remarrying? What if someone came in to celebrate his marriage to his second wife? What about plural marriages? I think the approach, from a legal standpoint, gets sticky when you say that it is the morality of the marriage that causes the refusal. It forces one to judge all marriages and that puts the business in a peculiar position. I do understand that a man marrying a man or a woman marrying a woman are grave sins and much more obviously invalid, but the courts don’t see it from our point of view because they do not rule by Catholic teaching. They rule by entirely secular laws. The law holds all marriages equal, therefore, the rest of us, legally, must do so.
The fact that this case is in Washington, where there is no sympathy for Christians, is unfortunate. I do not see it going the florist’s way.
As a florist or a baker, it may be that one must provide the service requested, regardless, and confess the forced participation.