Letterman’s monologue is not a nightly sermon full of moral lessons preached to politicians or the public. His stance is that of the proverbial court jester, a clownish figure with a mandate to prick the powerful — not set himself up as a model of virtue.
Could Letterman’s misbehavior be compared to the disreputable legislator who ranted and railed against homosexuals, and worked to deny them the right to marry and other civil privileges — and then was caught soliciting anonymous sex in an airport men’s room? That’s socially destructive misconduct with the potential for inflicting harm, pain and injustice on a portion of society and on society at large. Letterman’s misadventures contain potential harm, pain and injustice only for the individuals specifically involved — and since there have been no allegations about the sex having been nonconsensual or any partners having been underage, it’s all unpleasant but hardly some sort of threat to the public welfare.