Fear and loathing
If you grew up in the 1950's as a member of the LGBTQ community there was a strong likelihood that you weren't self-accepting. That black and white world would have led to believing you were a product of deviance and abnormality. Hence it was in this particular incubator that people like Ray Blanchard and Anne Lawrence would have developed their thinking on their own situations and what they signified.The trans as illness model (and for that matter homosexuality) is in fact largely a product of baby boomers and their vision of what normal is, and the idea that transsexuals are the product of sexual deviance rests largely on their shoulders. Today's trans youth would vehemently disagree and with good reason as they were spared the corrosive programming.
You will note that the challenge on my AGP page has still gone unmet which is to provide me with ironclad proof that transsexualism (in particular for gynephilics) is rooted in sexual perversion. The fact that it has gone unanswered speaks volumes, because the problem for those true believers is that the evidence just doesn't exist.