I think his definition (or perhaps mine) of what a crunch and what a sit-up is, is what's confusing me.
I've always thought:
1) Sit-Ups involved flexion at the hips. The spine is kept mostly neutral, the abs work to keep the spine aligned.
2) Crunches involved curling up the torso with the lower back remaining mostly in contact with the floor i.e. spinal flexion.
We ab brace first, elbows off the floor, good neck pattern, then curl-up against the brace just a little bit, not rising very much; then overlay deep breathing patterns. An incredible ab workout that spares the spine.
The quote above describes what I would call a 'crunch', which is great for the abdominals and doesn't involve a great deal of anything else. So I'm quite confused as to what exactly he has a problem with?
Which is strange, because McGill has a very good reputation in the industry. Part of where the confusion may come from is article you posted isn't written by McGill it just quotes him and others to make a point. However I get the feeling the McGill's quotes don't necessarily represent him fully.