With every political standpoint, there is a spectrum of supporters who support the cause - for varying reasons and varying intensity. It's very important to keep this in mind especially with issues like prop8 where the anti-prop8 branded the prop8 supporters as a whole as gay-hating bigots.
Here's the problem: we don't know where Eich fell on the spectrum. We don't know if he hated gays or if he was brought up in a traditional household where marriage is a religious ceremony rather than a love-based ceremony.
Hell, I recall some prop8 supporters whose only problem with gay marriage was that it uses the word "marriage", they were people who wanted civil unions to offer the same legal protections/rules as marriage, but wanted to keep marriage as man+woman so the concept of a marriage ceremony still had the same religious significance as it did before.
My whole point here is that we have no idea why Eich supported prop 8. There's a whole rainbow of possible reasons, many of them which are not quite as damning as people make out. Since we never heard the other side of the story, this whole fiasco looks like nothing more than a huge joke, but is actually a scary reminder of how passionate and defensive people can get over social issues.