The religious should not have a vote on issues of others' religious or irreligious thoughts, including policies which impose those thoughts on others.
This is why the Ten Commandments should not be displayed in government foyers (unless, of course, the comparable excerpts fromt he Torah, the Qu'ran, the teachings of Zarathustra, Buddha, Lao-Tze, and a few others are similarly displayed, which would not be a terrible thing. You'd have too include a little well-worded atheism up there, too, just to be fair.
In matters of civic discourse and policy, one's religious impressions should have no weight or play. Understanding this is, in my humble opinion, a key civic responsibility.
The area where this comes into conflict most frequently is in the adjudication of the governing by public code of morals. The simple way out of that is to leave all governments out of purely moralistic issues where harm to other citizens is not involved.