Yeah, I'm not sure how I forgot about the civil rights movement.
There's a fine line that has to be walked. Morality is always going to be legislated, it's just a matter of whose, so I don't buy the whole "You can't legislate morality" argument the way I used to. BUT I worry that when we start focusing on passing laws we'll forget that only God can change the heart. I really think that Prohibition failed because the church forgot to change hearts. I think that the only real solution to the abortion crisis is for Christians to work on changing hearts. We need to vote based on our values, but we need to remember that politics is not the solution.
Personally, I think we've lost the meaning of separation of church and state as originally intended. Originally, the colonists were afraid that the British would establish the Church of England in the colonies (there weren't many Anglicans early on around here), so there was a definite threat that the freedom of worship would be lost to anyone except Anglicans. What the Founders wanted to ensure was that there would never be a religious-based test for anyone to hold office, or to vote, and that the government would never be able to establish an official church. It's become "keep every religious expression out of the government" and "keep any political mention or support out of churches." that's where I have a problem, though I tend to agree that it's generally not a good idea to endorse candidates from the pulpit. Issue advocacy I have no problem with at all, until it becomes all that is preached about on Sunday. I grew up in a left-leaning Methodist church that constantly preached against the war in Viet Nam. My Dad worked for the Defense Department, and ended up not going to church most of the time because he got sick of it.
I've seen too many churches that lost sight of their mission because they got too involved in politics.
{edit to add}
Ironic that it's social activism (AKA social justice) that is the one place that everyone sees the church having a role to play politically.