Backing something that separates families is divisive and not appropriate for an organization that is about openness and diversity, especially given the current tech climate of monoculture.
Engineers can really be the worst offenders when it comes to hate-like views, I think in part because they're likely smarter than the average person so they've completely convinced themselves that they're the rational ones.
I remember back when I was at Google in 2008. A survey on lgbt issues went around company wide. What came back was so completely shocking and insane, especially out of Russia and India. Burn them, kill them, they don't desire to live, etc. And this was a survey you gave back to your employer!!!
Edit: as many people have missed my point let me clarify. The comparison against the KKK was simply to illustrate that who you donate to and support affects your organization, especially when that cause negatively impacts the personal lives of your employees (and goes against your org core values, and reinforces an existing problem of monoculture). I'm not saying prop 8 == KKK, I'm showing that personal beliefs matter when you're a leader.