Weighing in late, and not having researched this whole thing, my take is this:
First of all without the back story we don't really know whether this was harassment or not, and whether or not the firing was an overreaction. It could be either way, depending on the way people actually behaved.
But if a co-worker was haranguing another co-worker about the immorality of his/her marriage, then it's really inappropriate, assuming that the marriage itself is legal. It's inherently inappropriate whether or not the person doing it is a better person, using reasonable arguments, in the majority, or even just plain right.
It's pretty common for people getting married to talk about it at work or elsewhere. Plenty of places would routinely have gift pools and the like for newlyweds, and nobody would suggest that this sort of thing is foisting their personal choices on their co-workers. If that's all that was happening here, then harassment might well be the case. If there was more involved, then it's quite possible that the firing was excessive, but if you approach this as if it's inappropriate to talk about one's impending marriage at work, this would certainly be a new and different rule, and if you interpret it to mean that only heterosexual marriages should be talked about at work, then it's discriminatory, whether you think it is right or not.
There are still people who believe that interracial marriage is immoral and against God's will. Just recently there was a pretty notorious case of a judge in Lousiana who refused to recognize an interracial marriage because he was convinced that a mixed race child can't succeed in this country (talk about cognitive dissonance!) It wasn't that long ago that mixed race marriages were illegal in some states, and people argued against their legalization on religious and moral grounds, with passion and conviction.
If the marriage in question here were a mixed race marriage, would you approach it the same way? Where would you draw the boundaries here?
Gay marriage is new, controversial for many, and problematic for many, but it's here, at least in many places, and I think it's going to take a long time for people to get used to how to handle these situations. Until then, I expect that there will be excesses on both sides of the question, and it's going to be difficult to sort out who is in the wrong when there's confrontation.
