It's Never Your Fault
If there is a wipe the odds are it is not the healers fault. Assuming you are doing your job, as in healing people, then if there is a wipe it is most likely the fault of someone else.
Even when it is your fault, it is not your fault. You went OOM? Well, if the DPS got the boss down faster you would not have went OOM. It is the DPS that are at fault, not the healer.
If people took too much damage causing you to use your fast expensive heals it is not your fault, it is theirs.
If they tank is taking too much damage where you can just not keep up then the tank needs more avoidance, that is not your fault.
Reason # 2:
Healers Get More Respect
I've tanked, healed and DPSed randoms so many times I lost count ages ago. No matter what role I've played I've noticed that healers always seem to get more respect in a dungeon, assuming they are doing what they are supposed to be doing.
A healer DPSing and having someone die will not exactly win the healer of the week award. Outside of that, healers always get lots of respect in dungeons, even when they are not very good at what they do, as long as it looks like they are trying.
When you get to a boss where someone asks for it to be explained and they are a tank or DPS they might get kicked if the people in the group are jerks, if it is a healer that asks, they will just say to heal people and avoid stuff and move along.
When someone explains a fight, if it is a DPS they get attitude because they are just a DPS they know nothing, if it is a tank they get thought of as being an arrogant prick even if they are not, if they are a healer, people listen.
If after a wipe a tank or DPS says, you need to avoid that spell or it will kill you people will give them attitude. If a healer says, could you please avoid the spell because it is not possible for me to heal through it, people will make an effort to avoid it and even thank the healer for pointing out that it could not be healed through.
Reason # 3:
Better Players Make You Look Better
While that remain true of all roles, good DPS will make the tank look better, good tanks will make the DPS look better, good players as a whole make the healer look better. It is more noticeable with healers.
I've been in runs where everyone was doing 17K and they made me look like a horrible healer because everyone was taking so much damage it was impossible to keep them up (they where bad players, flat out) and I have been in runs with people pulling 8K at most (in a Zul we finished with no wipes) and I ended all fights at nearly full mana because they were good players and knew to avoid, interrupt and anticipate.
Example one, I get called a horrible healer because I can not heal 3 people who all think they are the tank and who all love to stand in bad stuff and never interrupt anything because it might effect their uber DPS.
Example two, I get called the best healer they have ever seen when in truth everyone was just doing a good job, there was little, if anything, for me to even do. Just heal the tank only and it was actually super easy. They just made me look like a super healer.
Reason # 4:
Saying You Can't Do Something Does Not Make You Bad
If a tank says he/she can't tank something, they are told to get better.
If a DPS says they can't do something, they are told to get better.
If healer says they can't heal through something the tank and DPS need to adjust to avoid, interrupt or mitigate it. There are things that can't be healed through and everyone accepts that.
Reason # 5:
No Loot Drama
Most groups have a rule to gear up tanks and healers first. As such when a piece of gear drops that a DPS might have a need for that a healer has a need for as well, the healer gets it first. Simple as that. You might need to role against another healer but it is better then having to role against a bunch of people.
Also, from my experience, healers are much more likely to share among themselves. If there are three healers that need an item they will usually let the person that needs it most get it.
Reason # 6:
Challenges Come In All Shapes And Sizes
When you start to over gear content you tend to be more lax about what you do. Tanks blow fewer cooldowns, DPS don't move as quickly or even at all from bad stuff, things like that. Which means as you get better gear your work can actually get harder. No other roles can say that one.
If everyone is still doing the right thing you can now challenge yourself to see how much DPS you can rock while still keeping everyone alive giving yourself another challenge.
Reason # 7:
Healers Get Cut More Slack In All Aspects
Die to an avoidable mechanic? Bad tank, Bad DPS, healer just needs to say, sorry, was trying to keep the tank up and they are cut some slack.
Die to some adds eating you alive? Not your fault, you have to heal, you can not stop healing or people die. So pulling aggro is never your fault.
DPS dying left and right? Not the healers fault, they must have taken avoidable damage.
Reason # 8:
You Can Fake It
Ever find yourself in a fight you never did before? As a tank, it could be deadly if you do not know when to blow cool downs or know what to avoid. As a damage dealer your DPS will surely be lower when you do not know the in's and out's of a fight yet. As a healer, heal people, avoid stuff, it is the same as every other fight you will ever do.
Sure, some tricky mechanics will come into play once in a while but over all the job of a healer is the same in every single fight they ever do. What needs to be interrupted? Not the healers job to know. What needs to be side stepped as a tank? Not the healers job to know. Just go with the flow and use basic common sense and you can fake it through any encounter you do as a healer a lot easier then in any other role.
Reason # 9:
Even Small Upgrades Feel Like Big Ones
You get an upgrade as a damage dealer and it makes your expected DPS go up by 30, woohoo. You get an upgrade as a tank and it makes your avoidance go up by 0.2%, whoop de do. You get an upgrade as a healer and it has a whole 10 more spirit and 30 more haste. It makes a difference. Really, I am not kidding. Even small upgrades are more noticeable as a healer.
Reason # 10:
There Is Always Something To Do
Ever try getting into a pug as a DPS? What is your item level? Have you done the fight? What is your DPS? Gearscore? Achievement? You name it, I am surprised they do not ask for a copy of your birth certificate and social security number to apply for a spot in a pug as a DPS.
Ever try getting into a pug as a Tank? What is your item level? Do you know the fight? Less questions than a DPS would have to endure but still some questions.
Ever try getting into a pug as a healer? No questions, just whisper them saying you are a healer and the invite comes. They do not look at your gear, or ask if you know the fights, they do not care. Hell, they do not even look at your level if you are a healer.
Go test it out, it is fun. Roll a priest on a random server and sit in trade, when someone says they are looking for a healer for something whisper them that you are a priest and wait for the group invite. Nice, a level 10 going in to heal Cho'Gall. I see a real success story coming from this.
I've had this happen to me countless times. I would be leveling a different character and say I have a priest and they would send me an invite on that character. One time my level 36 warlock was invited to heal a VoA run. Not kidding.
No experience needed, no geared needed, no skill needed. Healers get invites to everything easily. Of course, once you get in you need to make sure you do not look like a fool or you will be kicked, but healers will always have something to do, they will always have a shot even if they do not know the content, and they will always be given the benefit of the doubt and allowed to run in lesser gear, just to have a healer.
Now that is why playing a healer rocks.