Any program on television or radio must be examined for its sourcing.
Just like a radio station that plays a song you dislike, anyone if free to change the channel on TV or radio.
I don't think talk radio needs any warning labels. Listen, or not, but I hardly think anyone is "fooled" by what they listen to.
Rush comes from one point of view, Franken from another. Listen to what appeals to you, or to what the opposition is saying...or nothing.