"Reductio ad absurdum"
I wish it could be dismissed so easily.
You can go through the nearly 14 years of discussions about sholder holsters here at TFL and find those very arguments, especially the one about blowing your arm off at the elbow and having the bad guy come up and strip your gun from your shoulder holster.
And not just once, either, but numerous times over the years, and some resoundingly silly scenarios have surfaced to "prove" those fears.
My all time favorite was probably the guy who claimed that the second I reached for a holstered gun the (obviously) 97th level ninja master facing me down, Sensi Hoo Flung Poo, I guess, would use his thumb knife to amputate my arm and would then take my gun.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.