Note, this is a post I made on MMO-Champion about when it is right to hit "need" or "greed" in Looking For Groups such as LFR or LFD. My stance is as follows. (Note: Because we are 3/8 heroic, I normally only do LFR on alts if I need a specific piece, a friend needs a piece, or for the valor)
Link to the original article can be found here. http://www.mmo-champion.com/threads/1065833-Is-this-right-to-do-in-LFR?p=15106597&posted=1#post15106597
I find everyone saying "No its wrong" to be rather humorous. Wrong according to what? Your sense of fair play? Ok, maybe, but if its going off a personal opinion, then you can't hold others accountable to your personal standard.
Wrong according to the rules? Nope. You can need on anything you are able to roll need on and be perfectly safe. A ninja is technically one who breaks pre-arranged loot rules outside of a blizzard-enforced environment (basically outside of any LFG).
Wrong according to the community? Maybe. Sure, there are basic "rules" some people go by, such as MS>OS but those are more for self benefit and the golden rule. Those aren't even always accepted by all players.
So whose rule of "right and wrong" do you go by? Do you invoke some religious backing, "Do unto others" or something of the sort?
What is the premise for saying anyone else is "right" or "wrong" "good" or "bad"?
Example, if a tank is an asshole or just plain bad (whether due to skill, or lack, or because he's being lazy or just dicking around) some may say I'm justified on rolling on a tank item I need for OS. Blizzard rules allow me to do so. If I win it, am I a "bad" person? If I was running that dungeon just to build pieces for my tank spec, because I can't tank yet, and I was q'ing just for that piece, do I have more "right" then the tank who was just running for valor and happened to need it as well?
Under what circumstances is a decision right or wrong? Am I sometimes a "nicer" person, giving a tank a piece I won fair and square because he asked me too? Maybe.
Then again, consider the problems in the system. Very few people hit pass in LFD. Most hit greed or DE. If I need something for OS, I'll roll need. If the tank/heals/DPS do as well, and its their MS, I'll probably give it to them unless I'm there just to gather that piece. You see, this way I remove the chance of it being DE'd or hoping I get lucky over people who just want the crystal or the vendor price. Is that wrong? Even if I'm considering others by passing it off if two people "need" it but its their MS, I'm still keeping it over someone who'd vendor. Most players would say that is acceptable, and "right" however.
It all comes down to your personal view. No one can say you are right or wrong, as long as you are within the rules. They may kick or insult, kicking is within their right to do so.
Now more on topic, why should bad/lazy/afk players "win" loot over those who "earn" it by better performance? I'd do the same thing as the OP. Blizzards system doesn't reward good players, or those trying to improve, so I will try to do so. Some may say I am wrong, some may swear, but this is within the rules.
Note: This is specific to random people in LFD/LFR not guild/friends where progression/friendship come first.