The idea that the "proper" touch typing technique is ergonomic is not unquestionable. I've read some forums about RSI and there were quite a few people stating they got RSI right at the time they started learning and using the proper touch-typing method.
It makes sense too. Without formal training your hands will assume comfortable positions on the keyboard and the writing technique will evolve to suit your hand size and your movements. This should be more ergonomic compared to strict rules, developed for type-writers, where you have to press each key with the same finger every time, and where typical programming keys (brackets, colons) are left to the smallest finger.
What is comfortable initially is not guaranteed (or even likely) to be repeatable thousands of times. Look at weight lifting - if you ask an untrained person to lift a barbell or heavy bag the way that "feels natural", they'll probably lift with their back or do something else that would cause major problems if done repeatedly over the long term.
It makes sense too. Without formal training your hands will assume comfortable positions on the keyboard and the writing technique will evolve to suit your hand size and your movements. This should be more ergonomic compared to strict rules, developed for type-writers, where you have to press each key with the same finger every time, and where typical programming keys (brackets, colons) are left to the smallest finger.