The reason it is hard for me to accept is because, as I say, the grind is brainless.
If you were just given all the best stuff for free, would you enjoy it? No. The implication is that you have earned it.
Except grinding is not a skill-based task for which 'earning' is really appropriate; it is just so much mouse-clicking, effectively hazard free.
If there was actually any skill, imagination or genuine gameplay involved it would be fine. As it is... you are effectively being duped into thinking it is a worthwhile experience to pay money to do nothing but click a mouse button thousands of times in order to get stuff which will do nothing other than make your mouse clicks slightly more efficient.
Without things like storyline, setting and atmosphere, these games are creatively bankrupt, and that is why support for grinding and ignoring everything else worries me. The ONLY part I understand- even though I dislike it myself- is doing it as a competitive edge, as something to play against other people. But even there, Guild Wars quickly realised- after heavy demand by its players- that GRINDING to get better at PvP was insane (because it simply imbalances PvP immediately, like having a chess game where one side has two queens), and instead let everyone imemdiately do PvP on the same power level, separate from their role-playing characters, if they wanted. All the super-powerful stuff you get from storyline in Guild Wars is actively unavailable in its PvP, which is a purely skill-based activity, which is partly why it is so enormously popular.
So again, I see no intelligent justification in what you say. There is, in fact, a very high demand for a more interactive experience and better storylines from these games. Warhammer said it would do it (not sure how successful it was), SWTOR is doing it, FFXIV purports to be doing it, and the Guild Wars franchise has always done it (even though Arenanet was surprised by how popular the storylines were). So don't go saying that the mindless grind is actually what everyone wants, because that basically insults all of humanity. These games would not be one fraction as popular as they are if they were just grind and nothing else.
In short- saying that Aion is grind-heavy is a legitimate criticism. It is likewise understandable to be completely aghast at people that ignore all the setting and background of the game in favour of glorifying the gameplay void that is the grind.