After reading and experimenting more, I coming to the conclusion that almost all running problems, injuries, etc., stem from one central issue: overstriding.
In the last post, it was shown that both forefoot and rearfoot runners experienced running injuries. Clearly, just switching to a forefoot strike alone then doesn't guarantee proper running form. But the study showed that rearfoot strikers had twice the injury rate of forefoot strikers. Why?
My thought is that heel-striking is a more severe case of overstriding. While you can overstride with either a forefoot or rearfoot strike, I think the heel strike is a clearer case that the lower leg is being thrown ahead of the center of mass.
As to the cause of overstriding, the cause seems to be pretty clear: shoes! If you look at various studies comparing barefoot versus shod running, putting on shoes leads to a larger stride length and a lower cadence. With shoes, a runner is taking fewer, larger strides.
This is not to say that a person can't overstride in bare feet, or that they can't wear shoes and not overstride. I'm saying that wearing shoes while learning to run can prevent a person from learning to run with good form. Yet even if you learn good form, wearing shoes can still disrupt things. In the Lieberman 2010 study , for the recently shod Kenyan adults who ran shod during the study, some changed into heel-striking (and this is after a lifetime of mostly barefoot running).
Also in the Liberman study, for adults who grew up shod and then ran barefoot in the study, the majority still ended up heel-striking even though they were barefoot.
I would then conclude the following:
If you are running in shoes, you have to cautiously guard against overstriding
If you are running barefoot but grew up shod, you also have to guard against overstriding
If you grew up barefoot and then you run barefoot, you're probably okay!