It’s a fascinating example of motivated reasoning. Bill Maher has been raked over the coals on his irrational, anti-scientific attitude towards vaccines; his own guests have scorned his views on his own show; he’s been confronted repeatedly with the evidence and the rebuttals. He’s got to know by now that there is no rational justification for claiming that vaccines or thimerosal cause autism, or that the drug companies are profiting hugely by including poisons in their vaccines (which makes no sense, even if you do believe in greedy pharmaceutical mega-corporations).
So what does he do? He invites anti-vax crank extraordinaire, Robert F. Kennedy Jr., to sit around and commiserate with one another about how they’re called cranks and liars for merely denying the scientific consensus.