As a Christian, I can't dismiss any true part of the Body of the Church, but I can point out misguided or false teaching, and I am duty bound to point out dangerous teaching. I have my problems with some political crusades taken up by so-called conservative Christians but that is not the point of this post.
The problem with the Christian left is that, by and large, faith is just an affectation for them--an accent to their political beliefs, rather than a life-transforming relationship with Jesus. (I warned you about the broad stereotypes) Why do I say this? Because they so readily surrender any aspect of the Word of God that conflicts with what the secular authors of their political faith have written. Anything that embarrasses them in front of the Richard Dawkins of the world they want to get rid of, they want to be the crowd-pleasing, unoffensive Christian. Somebody who is unwilling to call a sin a sin.
They cherry-pick what verses from the Gospel they can to paint a hippy-like picture of Christ. Rather than provide a variety of links, you can just look for left-wing Christian sites and articles yourself. I've seen God's call to care for the poor and needy as "Biblical evidence" that God favors a large welfare state. This is no different from assuming that God wants the police to break into peoples' bedrooms at night to make sure they aren't touching themselves. In both cases you are taking something God said about our own moral behavior and turning it into government policy. There is simply no Biblical basis for that.
It is this itch for egalitarianism, socialism, collectivism, statism, whatever you want to call it, that forms the lens through which they read the Bible, if they read it at all. When you read a book through a lens, rather than with an open mind, an open heart, and lots of prayer, you simply see what you want to see, nothing more. You ignore what you don't want to see, you come up with reasons to ignore it.
"It was written for another time."
"We don't know who really wrote it anyway."
"You have to read it in context."
"I don't think it fits with the Jesus I know."
I have news for you, fellow Christian, if "the Jesus you know" is telling you that the Bible isn't really God's Word, then that isn't Jesus.