Tann--I echo your earlier comments on people misunderstanding of how science works and how scientific conclusions are formed over time and via repetition of experiements and studies.
This "debate" reminds me of something I heard (Again) yesterday:
"You can choose your own opinion, but you can't choose your own facts."
What galls me the most about people like those in the IF group is the sheer, wanton arrogance to disregard approaches that have a proven track record of success with others.
AN approach doesn't mean the ONLY approach. We don't know enough about human biology to understand the intersections of genetics and the emergence of various diseases/ailments (or not). For example, we know that some people drink and do drugs and smoke and never get addicted or develop cancers, while others get "sick" right away.
Why would muscle-building be any different?
"Look son, there comes a time in every man's life when he has to make a decision. Do you want to be big, powerful, jacked, yoked-up, have women everywhere want you and men fear you . . . or do you want to do crossfit?"