Many people would agree that to use the word "gay" as a term meaning "bad" is disrespectful, or even homophobic. Only slightly fewer people hold a similar view of the word "retarded." However, there are also people who take a stronger position, according to which words like "insane" and "lame" are similarly degrading and inappropriate (I've heard these words described as "ableist").
Although the stronger position strikes me as incorrect, I can't say why. Is there any way to draw a distinction between the use of words like "gay" and words like "insane" as generally pejorative terms? Or will we one day agree that all such usage is comparable to racist or sexist language? What is it exactly that makes such usage problematic?