I believe abstaining from politics is considered a sin. I think it is our moral obligation to speak out against a government when they violate God's law. James 4:17 says as much.

"Therefore, to him who knows to do good and does not do it, to him it is sin."

We know abortion is not good, we know life is good, and yet, if we do not speak out against the wrong of the government condoning murder of unborn children, we are in sin. Same goes for homosexual marriage, which is supporting a sinful lifestyle.