I think there's a distinction between our "fired for being pregnant" issue (which, as a Catholic, I disagree with) and the "fired for symbolically displaying a conflicting theological philosophy" scenarios.
I think something that amounts to heresy is fundamentally different than other types of transgressions on the level of a pregnancy outside of marriage. One occurred in the past, the other is one of a continuing nature. If the pregnant teacher went around wearing a shirt every day that said "Sex outside of marriage is a good thing to do!" then I think we're starting to compare apples with apples.
Also, as Cartier said, a lot of religious people (most?) are pretty good about actually treating members of other religions fairly and with dignity, despite what they believe may happen to them in the afterlife.