Questions in regards to Squat

I was warming up with full range of motion (ROM) body-weight squats, squatting as deep as I can with my knee extending beyond my toes. One trainer came over telling me that it's bad for my knees and it's not safe - I should be doing half squats and knees should be behind the toes instead. Knowing his background, I believe he's speaking from the input of a certain textbook.

So I explained my point to him that I opt for full ROM + knee extending beyond toes as I believe in getting full functional range of motion and with knees extending beyond the toes are part of natural human movements. While I also told him that he was not wrong to say it's bad for my knees.

According to Kreighbaum (1996) deep squats with knees extending beyond toes are absolutely fine. However there are 3 concerns to look into; (1) Speed of descent, (2) size of calves and thighs, (3) Strength of controlling muscles. Let's see what he has to say;

The primary danger to the knee occurs when the tissues of the calf and thigh press together altering the center of rotation back to the contact area creating a dislocation effect. The danger of knee injury in this situation may be prevented if either of the following factor are present:

• center of gravity of the body system is kept forward of the altered center of rotation 

• muscles of the thigh are strong enough to prevent the body from resting or bouncing on the calves.

Kreighbaum concludes the deep squat is of little danger to the knees unless these variables and factors are disregarded

The reason I told the trainer that he was not wrong is because it would be dangerous for me, IF I neglected the mentioned concerns by Kreighbaum. Noticed the IF ?