More specifically, to recreate Eden. What idealist liberals fail to realize is that Eden--the mythical paradise where Adam and Eve could exist without a care in the world--is fundamentally incompatible with human nature. People have an inherent need to do something that matters. When the only thing Adam and Eve could do that would matter was eat the fruit, that made it inevitable that they would do so.
Unfortunately, liberals keep trying to recreate Eden without recognizing that if even God couldn't get it right the first time, there's no way they ever will either.