Let's look at some common examples of perspective 1: Squatting and lunging are bad for the knees. Deadlifting is dangerous for your back. Overhead pressing is bad for your shoulders. You should NEVER squat past parallel. Olympic lifting should only be attempted by high level athletes.
Individuals with this perspective tend to be unfamiliar with the progressions necessary to become proficient in these movements. They also demonstrate a lack of confidence in the ability of human beings to LEARN movement tasks and set artificial limitations on human movement. Moreover, these individuals tend to view exercise progression as increasing resistance and volume with simple movements, as opposed to moving from simpler to more complex movements.
Perspective 2: All people have the capability to develop competency in complex movements by going through appropriate progressions
Although, pain and injury does occur when performing functional movements such as those mentioned above, it is inappropriate to jump to the conclusion that these activities are the CAUSE of pain. That line of thinking is similar to saying that since many people have knee pain with walking, walking must be the cause of knee pain, and therefore should not be practiced due to the stress it applies to the knees. This example sounds ridiculous but is really the same line of thinking as not training other functional movements due to fear of injuring oneself. The problem with the training of complex movements is not the movements themselves but the quality of the execution, and most importantly the understanding of proper progressions in training.
Let’s look at a common example: An individual that does not have the ability to get into a full proper squatting position using his/her own body weight would not be appropriate to squat with load (i.e. weighted back squat, front squat, etc.) or at high volumes (i.e. sets of 50 air squats). In this case the primary focus should be to work on the fundamental positions and transitions involved in squatting and only when that is adequate, should that movement be utilized in order to focus on strength and conditioning.
It is my opinion that the primary duty of any professional that deals with human movement, is to have a thorough understanding of how to teach progressions of functional movements ranging from the fundamental mobility/stability necessary to get into/maintain a position to the use of heavy loads and high velocities needed to strengthen and condition the movement. As far as pain/injury is concerned, it should be considered a warning sign that something needs to be adjusted in training. Positions/movements causing symptoms should immediately be assessed for dysfunctional patterns, and adjustments should be made to eliminate pain. If pain can not be eliminated with movement modification, referral to an appropriate health care practitioner is warranted. However, intermittent pain that is abolished with appropriate movement corrections can be utilized as useful feedback indicating improper technique.