As a healer, the only time I expect to be guarded is when we have consistently garbage DPS who run around aggroing everything and then dying and I get swarmed by trash. The rest of the time, any competent healer has enough (or should have enough) tools to deal with a single trash pack (aggro wipe, bubble, self heal, or just asking for one of the DPS to get the guy off / burn him down) to avoid needing guard.
90% of the time I'm out of guard range anyway, and so it does no good. So why do healers ask for guard?
Because, shock, some healers are bads. They fail to drop HoT's and bubbles at the correct time, fail to pre-hot before big hits, and try to half-*** DPS and end up aggroing trash onto themselves, then scream the tank sucks. Yet people put up with it because of queue times. Ugh.
Tanks should not be guarding healers except in a handful of specific , limited situations.
This. Absolutely this. As a healer I don't need to be guarded unless I'm getting pounded, which is rare, and I have HoTs, shields, and a threat reduction to play with along with the extra unwritten "kite" ability. to deal with incoming damage.