The flipside of the argument tho, is if the tank does drop then the healer rages that they didn't use enough CDs

It's much easier when the tank/healer know each other style's, i.e if the tank knows to trust the healer won't let him drop, or the healer trusts the tank to popping CDs sufficiently enough that they won't suddenly drop and so will know when to drop CS and stop dpsing.

As many others said, in instances where they don't know each other, you need to communicate, or get a feel for each other's competence. It is not the sole responsibility of the healer to keep the tank up, but a combined effort of both of them to make sure he doesn't drop.