I agree the squats are very good movements with free weights. Great for cross training. I have heard the knocks on machines but never took them too seriously. Started doing the leg press recently and realized it could really hurt someone either quickly by a slipped disk in the back, or slowly by the fact that it creates giant strength imbalances in the different parts of the legs.(no one sits on a toilet in the same fashion that a leg press machine is used). With this perspective, I now blame the meniscus injury sustained many years ago playing basketball on the leg press.
Moved straight over to the squat rack(for reps only no feats of strength).
