As a gay guy, I have mixed feelings about his resignation and I’m not sure it was a good thing for him, Mozilla or the gay community. It might have been better to engage with him, educate him about why same sex marriage matters, and help him understand why it is so important to the gay community. By forcing him to resign that opportunity has been removed or at least made less potentially valuable.
I don’t know Brendan Eich personally, but I would have been very interested in finding out exactly why he made that contribution. What motivated him? What was going through his head? Was it fear? Religious beliefs? Or something else? We will probably never know now, and I find that to be very unfortunate indeed. It’s very hard to build a bridge to someone when you don’t know why they have a particular point of view.