I am trying to analyze the issue. It's obviously a moral question not a legal question (because we're talking about sin, not about legality).
Being gay is obviously not sinful, because there is no choice. Getting a same sex marriage obviously is sinful, because you are going against the direct command of God. Officiating a same sex marriage is sinful for the same reason. Now, the state approves marriages and lends its authority to them. So, the state could be seen as an accessory. Presumably a voter would similarly be responsible, at one further degree down the line.
What complicates things is that you are not voting for an issue, you are voting for a candidate, who has views on many different issues. Another thing that complicates things is that you are not voting to create gay marriages, you are voting not to prohibit them. This may seem like a meaningless distinction, but if you believe there is a huge difference between action and inaction, this is key.
--
Congratulations to SuperNiceDog, Guru Winner, who was smart enough to pick
your 7 time champion, Link.