I must admit I have not read all the information stated here in this thread, but I just want to say that I agree with this being a silly emote.
As a priest I actually get offended when someone does an emote like that ... the healers of my former raidgroup actually refused to go on until one of the members in the raid removed an addon that did just that.
I can understand that people feel the need to shout for heals and that they think the healer has "forgotten" about them. I can only speak for myself when I say this, but I assure you that my eyes are fixed on those healthbars all the time when there is action.
Why do you not get the heal you are screaming for? Well ... _I_ am the one deciding who gets healed when and how they get it. A emote like that will _never_ change that fact, and a emote like that will only help to annoy me and possibly also the others in the raid/group with the continuous spam whenever your health hit that threshold. Who gets what of heals cooks down to a number of factors, but most importantly your role in the current events...if you are expendable that is too bad ... but that is just the way things are, deal with it and move on.
And to be perfectly honest ... the only thing the /healme emote show me about you, is that you deem yourself more important than anyone else!
I've used a couple of the /healme AddOns, and settled on AutoShoutOut. Not during raids, and rarely in a group. I just keep forgetting to check my health bar if I'm not playing a heal capable critter. It also sometimes saves the missus or I when we're mindlessly ripping up stuff and don't notice that one of us is getting well and truly pasted.
It can be useful to use such a thing if you're healers are as ineffective as I likely am, or if you're low on the triage list - not to let them know, but to remind yourself that you should be shedding aggro, changing to a defensive posture, using a healing potion or bandage, or just getting the hell outta the AE. In other words, undo whatever you just did! AutoShoutOut still works, and you can set it to only spam yourself, and not your raid or party. You can also choose audio or text only, and other events to alert too.
And lastly, I wanna echo that your health bar is your own responsibility and your local healer is doing his or her dam* best to support you and your group. At the same time - and for the same reasons - so is yer dam* aggro. Tanks do their own form of triage, too. Replace the word "heal" in previous posts with "taunt", and you'll get the general idea. ;) (Oh, and ... if you kite it, you're the new tank. Gratz!)
Or even better - sets the alpha to 0% on the spammer...
Might be better to even have an addon that selectively removes that text. Those addons use 'stock' text, so you could have an addon that parses chat, and removes that one line completely. No need to ignore.