Wow, this author's really opened my eyes. Since there are no erector spinae muscles, deep vertebral extensors, lats, traps or ab muscles, and since bones do not adapt to loads, he's absolutely right: squatting is a terrible idea!
He's even right about leg presses. Since you don't pin your body between a seat and a sled with opposing forces coming at you from both directions, and since there is thus no load through the back, leg presses are fully safe on the spine.
BRB guys, I'm going to go start a revolutionary leg extensions/leg curls superset program. I'll be teh greatest.