Well, regardless of who these proponents are, or what their credentials are (or lack thereof) – they are wrong. Here is why.
A). In the case of items #2, 3, and 4 above, preliminary body shots will not solve the problem. Sure, if you are set upon unexpectedly and must react suddenly, the burst to the chest is the best default as it is faster, and easily placed at close ranges regardless of the level of shooting skills.
But if you have prior understanding and information of altered mental states, armor, or it is evident that the scene unfolding before you is Active Shooter-based, or Jihad-motivated, trying to shoot them in the politically-correct chest is foolish, and may cost you your life.
B). Insofar as the Pelvic Girdle Shots go, it does not take a degree in medicine to realize that the pelvic bone is not connected to the hands, nor the brain, and that a pelvic shot – even if successful – will not stop a terrorist from continuing to fire, or setting off an explosive.
Medical explanation: The pelvis is a ring structure. It is exceedingly strong and people with broken pelvises in car accidents have in fact been ambulatory immediately afterwards. In order to break and destabilize the pelvis, it must be broken in two places.
Those places are near where the two pockets would be in a man wearing Levis. They are far smaller than the area suggested for a brain shot. So a proponent of the pelvic shot wants you to hit not one, but two targets that are smaller and harder to hit than the head shot’s highest value area…and two targets that will prevent neither return gunfire nor explosives detonation. Stupid idea, do not take such advice.