I asked my coach about this, and he said that he teaches some drills as a foundation (mostly to teach angle recognition and engrained responses) and then, after his students learn it, they can test it out in an alive format to see whether it works for them or not. Some can pull off the techniques, and some can't. Then they can keep or discard the technique based on whether it actually works, or even tweak it to make it work, without having to refer back to him. Teach a man to fish, and all that.
I don't think cultlike behavior is limited to, say, TKD. I've seen a lot of the same attitudes in boxing gyms, too. It's everywhere. There's a BJJ gym I know of that doesn't allow students to train elsewhere, and a local boxing gym where nobody ever spars (and I do mean ever). I know a Thai boxing instructor that doesn't allow his students to teach, even if they aren't teaching Muay Thai. I've also seen extremely healthy dojos (taijutsu, aiki, etc.) with people whose self-growth is evident, and I think they only spar during belt tests.