trust goes both ways. healers seem to have a love affair with letting a tanks HP get as low as possible before healing because they'd rather dps or they want a few % more efficiency out of Benediction or something. Many times they cast a heal too late then everyone is scrambling while the healer tries to raise and heal the tank while mobs are going everywhere.
Why should I trust random healers when they've taught me I shouldn't? If me not wanting to be dead and casting clemency offends you, too bad.