Eich was not anti-gay, he was anti-civil rights. Legal marraige and religious marriage are unfortunately poorly named, but two very different things. If Eich doesn't understand that, he's got bigger issues than being dumped by Mozilla.
I have plenty of good friends who do not agree with the idea of homosexual religious marriage and yet support civil rights and the right of homosexuals to be legally married.
That said, cable news, groupthink and information overload have a nasty habit of making us fall back on baser instincts (gay=bad, Christian=bad, war=bad or any other black/white arguments).
Instead we should probably turn to our communities where we are able to have long-form and less-aggressive arguments about fundamental issues. If you perceive the person you're arguing with as a human and a friend, you're less inclined towards unmitigated anger and senseless aggression. But that would require us to put down our computers and walk into town hall and actually speak with humans, so I'm not holding my breath.