Same as divorce and premarital sex. Became normal in the society but not supported by most Christian denominations. I do not believe that any church will be “forced” to perform gay marriages but there will be many willing to do so.
Name one denomination which won't marry someone who is divorced.
I pray you're right on the first account and hope you're wrong on the second. Unfortunately, I too believe some, if not many, churches will be willing to do so.