You seem to be getting to the wrong conclusion from the right arguments.
First I want you to remember that you're asking tanks to do something that is not a necessity to improve the comfort of the healers. Keep that in mind.
I disagree when you say that healers have it hardest of all roles but that's my personal opinion, I find that being the tank requires more attention to the mobs, my position, my teammates, their position, the mechanics of a fight, whatever.
I can't trust people I don't know straight away. I'm not going to start immediately with large pulls in a dungeon, I need to see who I'm playing with. How much damage can the DPS dish out, does the healer contribute or not (there are still many dps-shy healers), does he still heal beyond that, etc.
I judge people. I have to, I'm the shield of the group, the one going first, and I'm the one supposed to get hit and stay alive. You might think that it's the healer's job to keep me alive, and it is, yes, but ultimately the tank is the one to decide how much they can get hit and survive. This is a tanking reflex from playing years of MMORPG that most dedicated tanks have: "If I die, we wipe." Not necessarily true but that's not the point.
So I don't know whether I can trust my healer, and life can go down very fast.
I see my life draining away, I pop a cd, but maybe that was panicking for the healer, maybe he's good and concentrating on DPS and only making sure I get healed when I hit 10%. Couting on me not to die by using those CDs. I don't want to be forced to resort to a CD for something that I judge not necessary.
This is possibly the point I disagree with you most: my defensive cooldown abilities are not comfort abilities, this isn't a healer quality of life improvement. They have a point and need to be used to an end.
Never would a situation get messy because I withhold a cooldown. That can't happen. That's the entire point of these abilities, to prevent disaster when error strikes, you can't say that it's an error in itself to withhold them for that.
Situations never get hairy because I do what I do as a tank and pop my CD when they're neededs, not just because they're available and unused and we might gain 10 seconds on a fight.
If you want to rush something you're over-geared for, sure, let's use CD because it doesn't really matter and the healer will be able to deal damage. Real content ? Not happening.