Will Churches be forced against their will to perform such marriages
I would think not. Churches are private entities with voluntary membership and as such would be free to conduct their business as would any private club. I'm sure some churches would perform them voluntarily but I can't see how any could be forced legally to do so.
The issue is whether gays are entitled to be married in a manner that is officially and legally recognized. I fully understand that religious people see marriage as a spiritual thing sanctioned by God and consider the exchange of vows standing in front a preacher as the moment you are married. I do respect that. But from a purely technical and legal standpoint you are married when you and your wife sign that marriage license. I can see how a church can legally deny them the ceremony. I can't see how as a society we can legally deny them the license.