Or we could see it as it actually is. Everybody who comes into the store to buy products or a service the merchant has for sale is provided those products and/or service. That has never been an issue in any of these cases.
But if the merchant has for sale wedding cakes for Christian weddings, does it follow that the mechant HAS to also carry wedding cakes for NAMBLA or white supremacists or the Westboro Baptists or any other group engaged in activities or promoting docrine that the Christian cannot condone or support? Or create any other product for such groups that the store does not routinely have for sale? Most especially if the Christian is forced to go to the customer's premises and be seen and participate in an activity the Christian finds offensive or cannot condone? Must a Christian accept everybody and everything in order to practice his/her Christian faith?
Things are never as simple as we sometimes would want them to be.
In the case of wedding vendors; bakers, DJs, photographers, caterers and etc., they do not 'participate' in the wedding. They are not invited guests. They do not officiate durning the service. Their merchandise imperamator is not required to legitimize or confirm the actual marriage. Could you imagine your marriage hanging on the approval of the person who bakes your wedding cake?
They are, in fact, merchants who operate public businesses, that is to say businesses open to the public.
Any refusal to provide their normal services is tantamount to discrimination.
What is to stop such merchants from expanding such discrimination to inter racial couples? As it is legal for inter racial couples to wed, and as it is not a crime to merely be an inter racial couple, discriminating against them is patently illegal and morally wrong.
It is not illegal to merely be a homosexual. A majority of states recognize marriage equality. Why should homosexuals suffer under the bigoted discrimination of merchants who clearly have not thoroughly read their Bibles?