I think you have to be a little more specific. If
merely removing a former legal right is evil, who
were the bad guys when a Maryland referendum removed
the right to own slaves
I think the answer to that is clear if you subscribe to the principal that one person's rights end where another person's rights begin.
It's certainly true that the slaveowners had the rug pulled out from under them in a sense but their legal right to own slaves infringed (to put it mildly) on pretty much every single human right the slaves had.
With same-sex marriage, on the other hand, it's very difficult to see how one person's consensual marriage could possibly infringe on another person's rights.
Also, if the correct position is that marriage in any
shape is a legal right, are we going to crucify people
who made polygamy illegal?
You're absolutely right: the polygamy question is
very tricky. I can't give you a single objective reason why it shouldn't be legal.[1]
It's incredibly fallacious, though, to suggest that same-sex couples shouldn't have the right to marry simply because there's another tricky marriage-rights question out there. (If we discover that there's a wrongfully-convicted person serving time in a state prison, should we make him stay there because we haven't figured out what to do with the prisoners in Guantanamo Bay?)
are we going to crucify people who made polygamy illegal?
I'd say that we should consider their views in the context of the times in which they lived. The human race has come a long way in the last couple of centuries in terms of recognizing human rights.
Hopefully some things that you and I believe today will be viewed as positively caveman-like in 200 years. That's the price of progress.
I'm bothered by people adopting fashionable causes as a
reason to hate people who don't believe in them
This and the "crucify" thing are really straw man arguments. I'm certain there are some exceptions out there but during the entire Eich/Mozilla public debate, I didn't see anybody (certainly not anybody prominent) claiming that Eich was a terrible person or that we should hate him.
I certainly don't hate Brendan Eich; he seems like a good person in general. Even if it was the right thing to do, which I think it was, nobody "won" that whole mess. The Mozilla community lost a great contributor.
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[1] I believe you should be able to legally designate whomever you like as a family member and assign whatever family-related rights you want to them. The government should generally stay out of the morality business as long as everything is between consenting adults.
From a purely legal standpoint, titles like "wife" or "brother" or "cousin" are really just titles that confer various sets of default rights and establish a default order of precedence for inheritance and power of attorney. (On a personal level those titles mean much more to me than that, but that's my business)