Rush has an excuse for his refusal to debate liberals on his syndicate radio show. Media Matters transcribed this statement from his 18 October broadcast:
What do I do on this program? I set up exactly what the other side's position is. I'm the only one who'll do it honestly. If I have a liberal guest on this program, I'm not guaranteed the liberal guest is going to be honest about what he believes. So in order to establish what I believe and what I think, I set myself up by presenting the liberal point of view on whatever issue it is I'm talking about. [emphasis in original]
What Limbaugh portrays as an "honest" presentation of the liberal point of view is a mendacious misrepresentation of liberalism, contrived for the sole purpose of attacking straw men rather than real liberals.
Limbaugh's honesty is on par with his responsible use of painkillers.