When I pug I never just assume my DPS know what they're doing. And I don't feel like spending some time grilling them about kill order. So I tend to just put Guard on the healer because I assume I'm the only one with any sense. I'm often right
"Often right"? No, you are not, if you think guarding healer helps at all.
Next time instead of reading just the first line, try reading the whole post.
Do I really need to explain it again?
Healer will ALWAYS
have aggro on any and all mobs that neither the tanks or the dps are not doing any damage on, regardless of whether or not the healer has a guard on him.
Healer will NEVER
have aggro on any mobs that the tank OR dps are doing constantly damage on, regardless of whether or not the healer has a guard on him.
In either case, a guard on a healer will do absolutely no difference what so ever.
Healing threat is so low it is impossible for them to overaggro anyone else who has threat. The only time healers will have aggro is when they are the only one in the mob's threat list. It does not make any difference what so ever if you have guard on a healer to even further lower his threat, because if they are the only one in that target's threat list, they are still on the top of the threat list.