I think opinions and teachings like the above can be very damaging to impressionable, confused teenagers. I speak from first hand experience with my 17 year old brother who put of the blue announced last year he was transgender.
It became apparent that a "friend" on the internet had been encouraging this opinion and pushing him into it. He then researched the best things to say to the doctors to begin treatment. I told him if these feelings were genuine he wouldn't need to research the best answers!
Our mum had been ill with cancer on and off for 2 years and spent a lot of time in hospital. He was confused, impressionable and quite possibly confused about his sexuality not gender.
1 year later luckily his treatment never began and he's happily living as a male.