"What's so wrong with those beliefs?"
There is nothing wrong with them and I don't think Warren is criticizing them. In fact he believes strongly in them as his writings show. The context of his statement is Christians acting in the world to help those in need. What he is saying is that modern day fundamentalists are known more for what they are against than what they are for. They have separated themselves so much from the hurts of the world that they have abandoned the stage, except for the abortion issue, to the liberals and social agencies. I don't think he was criticizing the five Fundamentals but the lack of Christian praxis in the Fundamental churches.
he says they are narrow and legalistic.