Nothing corrupts intellectual power like the abuse of the language. Free speech becomes an endangered species when powerful words, misused, become shortcuts for specious argument and repetitious cliches trivialize noble ideas.
Nothing stops someone in a foot-in-the-mouth defense of himself like being told "you're in denial," meaning that he's avoiding the truth of experience. If you don't acknowledge an accurate diagnosis of a terminal disease, recognize the philandering of a mate or see the approaching death that awaits us all, "you're in denial." The truth-seeker in wolf's clothing demands that everyone look at the world through his lens, as though through a glass, lightly. Denial is based not on facts, but emotion.
All deniers aren't equal opportunity deniers, and an all-purpose stigma inhibits rational argument. We see this illustrated on Page One every morning. Skeptics of global warming are compared to Holocaust deniers. The ecologically correct become eco-heresy hunters determined to silence anyone who questions their evidence, flimsy and questionable or not. Any human destruction of nature is described as "ecocide" (like genocide.) When David Irving was sentenced to prison in Austria as a "Holocaust denier," an Australian journalist suggested making climate-change denial a similar offense. An Internet commentator wants global-warming deniers to be tried like Nazi war criminals.
"Denial" came out of the therapyspeak prevalent in the middle of the 20th century, especially as it was applied to confronting the reality of mortality. It was popularized as the first stage of grief, but was quickly expanded to include refusal to confront any bad news or disturbing ideas. Like the broken clock that's correct twice a day, denial is sometimes an accurate label for certain behavior, but as a consuming mythology in our culture it becomes the all-purpose description to deny independent thinking.
On a personal level it's used to accuse others of cowardice in refusing to face up to what is regarded as in their own best interest. It elevates a kind of psychological groupthink over independent interpretations and casts a critical eye at those who face their problems in their own way. This attitude wreaks enormous havoc when it is applied to public issues.