This is not so far removed from saying Mary Jones shouldn't be CEO of Mozilla because she donated to a campaign against CO2 emission restrictions: Again by analogy with a settled political issue, "She's denying Global Warming. You'd be OK if she denied the Holocaust?"
I'm not arguing against voting pragmatically, I'm arguing that calling opposition to same sex marriage akin to racism today is a nonsensical comparison. Maybe it will look that way in hindsight, but it's not fair to hold anybody to hypothetical future standards.
Of course we want to encourage as many people as possible to contribute and therefore anything that pushes large groups of people away (for no good reason) is bad.