That being said, I find it odd that you think no one can sincerely hold the position that someone's bigotry was/is abhorrent, however mainstream it was when they were putting money behind it (which is about as direct a piece of evidence that you can get).
I was alive and an adult as of 2008, and I didn't live in California, but I remember this situation. At the time, I was a somewhat naive young libertarian and my thought was that this was a great time to get the government out of the marriage business completely; leave marriage to churches and have the government only involved in the civil union aspect, which more naturally generalizes to gay marriage as well as certain conservatorship relationships or even polyamory, without forcing any cultural or religious shifts. So had I been in California at the time, I might well have voted for this measure, but I do not feel that I was a bigot for this, much less an abhorrent bigot. Since Eich never made and has never made public statements in any direction, we have literally no idea what his actual views on the subject were.