I sort of agree with this, but it doesn't mean he can't ask any questions.
Anyway, it's somewhat true that sex change operations can present health risks, perhaps on par with obesity (although both are too nebulous to really quantify). Obesity, however, can be 'fixed' whereas both physical changes and the underlying mental dissonance of transgenderism is with you for life. So as with above, I find the comparison between the two to be irksome.
Transgenderism is also more than just a sexual fetish. Although I would actually argue, having been in this community for some years now, that a lot of feedees do show characteristics of dysmorphia that are comparable to transgender people. That fact is probably under-appreciated by the rest of the world, because (unlike with transgenderism) feedists can hide the fact that what they do is intentional.
Also, there's a big difference between just any old fat person, and a fat fetishist. Yes, many people are overweight, but most of them don't like being that way. They have, somewhat understandably, no desire to celebrate it or strive for 'more acceptance'. So its only the die-hard feedists who can really be compared, even loosely. And they're not very numerous.
As for being a 'mental disorder', it's just semantics. Being left-handed was a mental disorder once. There's no actual biological reason that one sexual practice be a disorder and another not, aside from how unpopular or immoral it is.