I think the reason it's ridiculous is that if you distill the concept to "people would like their body to match their sexuality" then that includes almost everyone. Like I assume a generic straight man wants a body that his partner will find attractive, and also wants a body that can perform the typical male sexual role. If he goes to the gym and does some bench presses while he thinks about how hot his girlfriend will find him when he takes his shirt off, is he a crazy pervert who has an auto erotic target location error? Hopefully I don't get in trouble for this, but straight women do this to an even more obvious degree, because so much popular fashion/media has some amount of male-gaze type sexuality init.

Blanchard thinks that trans women (he never talks about trans men for some reason) are different than "regular" sexuality because we transition while doing the I-like-my-partner-to-be-attracted-to-me-in-w-eay-that-affirms-my-ideas-about-myself thing that almost everyone else does. Blanchard is unwilling to consider that changing your sex is about more than sex, so he thinks that trans women must have a uniquely intense version of this.