Some people can be quite narrow minded and seem to have tunnel vision on what they see is best.
The human body generally functions the same in everyone. Anatomy and physiology is explained in the textbooks like we are identical human beings. But we are not all the same.
We are all individuals and each persons body does not always react in the same way to the environment, medicine, or exercise. We cannot all expect perfect results from the textbook. We are all different. So what works for one person does not always suit another. That is why we should be open minded. We have to try things for ourselves to find out whether they benefit or not.
Getting to the subject of squats. Yes, a squat is a very good leg strengthening exercise. Taking the squat further than a ninety degree bend at the knee is debated as controversial/contra-indicated exercise. In a lot of exercise techniques we are continually informed that we should not take the knees any further than the toes i.e we should be able to see our toes beyond the knees, keeping in line with the toes.
This is to prevent taking the joint further than it's normal range of motion thus aiming to prevent injury.
Professional dancers, gymnasts, weightlifters, etc, they all perform lots of contra-indicated movements, they push themselves beyond the limits to get where they are and often perform very unsafe/dangerous movements.
You can take advice from anyone but you shouldn't follow it if you think it is harmful or dangerous to you. It is good to try different things though, it's the only way of finding out what is best for you as an individual.