I left due to a series of events that left me realizing that putting in the time to raid just isn't worth it (at least, not on my server):
- In Wrath, I was part of a semi-casual progression guild. We finally got to LK 25 only to have the RL buy a LK kill and start us over on heroic modes for gear. I didn't agree with the decision, so that coupled with a few other things (newborn, more demands at work, desire for more than three hours of sleep a night) led me to seek a more casual guild. Queue slight distaste of raiding due to the realization that I may not get to enjoy the game the way I want to because other people are so focused on gear.
- In Cata, I was raid leader for a casual raiding guild starting partway through T11. We downed T11 when the better raiders were still in the guild, but they all took a break partway through T12. I was told specifically not to worry about recruiting (which I hate doing and I am NOT the type of person that can sell...well...anything), but the recruiting officer wasn't recruiting either. We never downed Rag, and only got Hagara down once or twice before I quickly got fed up with half the raid dying to Hour of Twilight and/or Fading Light...especially with LFR was available as a learning tool.
- At the end of Cata I joined my last progression guild as part of the second raid team. At the beginning of MoP RNG sucked for me - if I remember correctly I was still sporting a couple of 430-ish blue pieces and a green trinket (still around a 460-ish ilevel), despite running twice as many heroics as everyone else in the guild (except one other person) and running LFR multiple times a week for bonus rolls on bosses I needed things from. When it came time to do MSV, another tank was taken that had gotten lucky with some epic gear and I was told to "do more heroics".
That, to me, was the last straw - I had already put in more effort than most other people in the guild, and was told to "work harder" as another person who decided it wasn't necessary to gem/enchant his epic gear got to raid to his heart's content. I put in a huge amount of time at the beginning of the expansion, only to see all of that effort be completed disregarded.
So, three "raiding" guilds in a row - each and every one ended up being a complete waste of my time. I found myself hating the thought of logging on to do a "real" raid, and with pugging all but dead on my server I just didn't have it in me to try a fourth time.
While I am doing strictly LFR now, I don't particularly enjoy it. Yeah, it was neat seeing the content the first time or two...but now it's devolved to "Oh god, please just let us one-shot all the fights so I can go do something else that's fun". I'm grateful that LFR awards gear that is relatively powerful - it lets me do a lot more of what I really like: soloing old raids.
As far as your bullet list of drawbacks (based on my experience, so completely subjective!):
Healer 10-15 min queue, Dps 20-60 min queue.
I can do quests/achievements while I'm waiting for the queue
Potential of;
tank fail due to pvp gear
Hasn't happened very often...at least, not if you get it done before Friday
Heal fail due to healers being in dips spec because they were too good for dps queues.
This has happened maybe one time.
DPS fail because of not following the mechanics that they know better than to do (AOE on DWing thumb)
This is the biggest problem in LFR that I've run into...after a wipe or two people usually learn or the Determination buff helps those of us that are paying attention pick up the slack.
Unenchanted/ungemmed/unforged/wrong gear/no knowledge of class/no knowledge of the encounter
Enchanting/gemming gear isn't really necessary for LFR. Before Friday, most people are good about learning after a wipe or two.
Afk players
If that has been happening, I haven't noticed it.
Players barely trying
Same thing as AFK players.
People who grief you because they are 1 in 8 million and no consequences.
This has happened a handful of times...not much you can do about it besides kicking them, just like any other area in the game.
Booted just because someone said "Kick X because of bad DPS!" When you were a healer.
When this has come up, people are usually good to say "uh, they're a healer..." Conversely, most people will point out a DPS/healer not pulling their weight in their role pretty quickly.
DPS in tank spec
Happened one time during Dragon Soul (and they won the trinket off Ultraxion QQ). Just like griefers, not much you can do outside of kicking them.
Huntards killing you with misdirect for shits and giggles
I've never seen this happen.
People screaming at you for tanking wrong
The only time I've seen this is when the tank is actually tanking incorrectly (taking a leisurely stroll between pillars on Lei Shin, not picking up adds, facing bosses with conal/cleaves at the raid, etc.).
People screaming
Doesn't happen that often, and when it does I can ignore it (or laugh at it) because I only have to deal with the morons for another hour or so.
SUB-PAR crappy versions of LFR gear.
I can do almost everything I want to with the LFR gear. Besides, I feel much better about being an almost Rank 10 brawler in "sub-par crappy LFR gear" while people in full normal-mode gear are still struggling in Rank 7/8.