It is commonplace by now that players who complain are not as likely to quit as players who don't complain. What seems strange at first is not hard to understand: players who complain care. Players who don't, just quit.
Now, that doesn't mean that you should hit barking dogs. Throwing Pandas at a player who complains about immersion problems in WoW can absolutely convince him to rage-quit. And as I already explained in a prior post, cognitive dissonance is a powerful effect that is able to keep players from playing a game even though they might actually like it. The more often you tell other people that you hate pizza, the less probable it is that you buy a pizza - even if nobody watches.
That having said, ignoring barking dogs doesn't usually make them bite. Players who complain about balance problems or too much downtime or trash mobs or whatever, don't usually quit. The reason they complain is that they really like the game. They care. A MMO with a forum devoid of complaints is a dead MMO.
There is one complaint, however, that needs to be taken very seriously:
This is the problem of WoW's questing game. Now, I'm certain there are a few players who like it, but I'd bet any amount that most players don't. Sure, some of them say that they never liked it. But don't believe them! They hadn't leveled their first toon if they hadn't liked the questing game!
I remember WoW's past. There were always complaints about the questing game: it was imbalanced, it was too slow, it had too much downtime, what have you. And there is nothing inherently wrong with tackling these complaints and trying to improve the questing game. But what must absolutely not be done is making it better by making it more boring. This is a critical mistake and it happened.
I complained about the LFD tool since it exists. And I think that I have a point when it comes to its deteriorating effect on WoW's ability to draw players into communities. However, I still used the LFD. And not just a little.
The questing game is different. It has become so incredibly boring, that I stopped caring. If there hadn't been a LFD, I had stopped playing much earlier - given the boring alternative. (Please don't quote that sentence out of context - thanks). As bad as the LFD was for the community, it has been a blessing considering the ridiculously boring questing since WotLK and especially since Cataclysm.
Blizzard didn't just make the questing faster and easier. I could arguably live with that. They made it boring. The amount of things that keep my mind busy while questing has been dramatically reduced. Once in a time it contained things like sneaking past mobs (even without being a rogue), trying to access chests full of treasure, hoping for useful drops, running away, evading packs of mobs and pats, killing fleeing mobs, etc.
Nowadays, I run to the arrow, I hit the highlighted mobs or click the sparkling *whatever* and then I return by following the arrow. It's so damn boring that I can honestly say that I didn't do it any more than necessary in my recent experiment - and even before that. No narrative, however brilliant, could convince me to level 20-90 by questing.
The fact that some players are really bad at the game and need to learn is true. But that doesn't mean that the game needs to cater only to them. Challenges that automatically adjust depending on the ability and mood of the player exist. It's not rocket science.
Stop thinking about how to replace the “kill ten rats” quests. This is not the real issue. The real issue is that killing ten rats can fail at keeping your mind busy. And if that happens, most players don't complain. They just stop logging in.