Would you not agree that almost anything can be taken to such an extreme that the extreme is crazy?
Yes, I would agree with that, and it applies to all areas of life from religious or political fundamentalism to people who dedicate themselves to collecting things.
But I'd also say that to apply the term 'craze' or 'fad' or anything similar to a serious, delicate, and really quite complex topic like transgenderism is quite dangerous and insensitive.
I haven't read the book so I'm not going to comment any more deeply on it's content because I just don't know.
I reacted solely to the tagline as many people will do. My reaction was to find it a bit worrying, but many other people will see that word 'craze' and without reading the book or any other sources of legitimate information on the topic will just use those few words to reinforce their uninformed views, taking it as confirmation that transgenderism is just a lifestyle, or a fad, a choice someone makes, which is a massive over-simplification. Massive over-simplifications often lead to misunderstanding, intolerance and prejudice.
I get the tagline, it creates reaction and discussion and draws people to read to find out of the author's viewpoint is really as simple as it implies. So I guess it's working well :-)