Religion and politics

I don't understand why the left is letting the religious right get away with being the "religious" right. If one looks at the lessons of the bible, the left is CLEARLY following the teachings of Jesus and the New Testament. Admittedly, the religious right does follow the bible, but it's the Old Testament that they revere.
I got into an argument with my mother one day about the relative "sinfulness" of various laws in Leviticus - you know the ones:

Don't eat shellfish, don't wear clothes of mixed fibers, men - don't sleep with other men (no prohibitions on lesbian sex - did you notice that - men are men no matter how far you go back in time, apparently), don't shave your beard, etc.

and Mom told me that when Christ came, he swept all of those laws (except for the gay ones) away. A few days later, she was talking about the 10 commandments, and I reminded her that when Christ came, all those laws were rendered null and void, remember? She, of course, insisted that she meant no such thing...
The point is that most fundamentalist, literalist evangelical Christians ignore completely the edicts by Christ to love your neighbor, support the poorest among you and "judge not" others. They tend to focus on the legalistic laws of the Old Testament. If a political candidate came out and confronted the religious right with that fact, they would win the moderate to left-leaning Christian base. I admit that it doesn't seem like there are that many of those types around, but I think that they are there - they are just being quiet because they don't want to admit that they follow the same religion as the right-leaning Christians.
This is, of course, just my opinion. I'm neither Christian, nor conservative, so my take on how to get Christian conservatives may be way off base - but I think it's worth a try...