No they shouldnt be forced to wed anyone they don't want to. Its still acceptable to refuse to perform ceremonies for divorced people on basically no grounds besides 'we dont agree with it'..so I dont
really see the difference.
Personally though, I would think any vicar that refuses to carry out a wedding either to a gay couple, or a divorced one, or any thing else (legal) is a bit of a douche, but its their choice to be a douche
Edit. After reading this I see niamh already made the divorce point...and also I agree with the why would you want to get married in a place that had to be forced to do it argument.