There are many people there saying that if your not willing to marry homosexuals then you need to turn in your credentials to perform marriages. In at least one province, any non-church officials who are unwilling to perform same-sex marriages were told to turn them in. There has been some protest in some places that ministers shouldn't get an opt out.
The question is similar to asking whether or not they would have to turn in their credentials if they didn't want to marry a mixed race couple? The answer is the same to both questions. As far as the minister is concerned, he is not a representative of the state but rather a representative of his religion. He is certainly free to say he won't perform marriages for certain people. I know that some faiths won't marry an interfaith couple, it is about the same.
Although on that note, I have heard that some countries (wish I could remember where) only civil unions are legally binding. If you want a church ceremony, you have to do the legal ceremony seperate. I'd have no issue with that.
I would certainly agree with you. The state either needs to get out of the marriage business altogether or make it a purely secular institution. For me it comes down to the issue of legal rights. Why do mixed sex couples get cheap legal protections under the law and same sex couples don't?