You think this works like the Prisoner's Dilemma
Yes, in one interaction, people can abuse the need / greed system and win. This is a game where one character will typically be played for a long time, though, and there are social consequences to ninja behaviour above and beyond
pure loot consequences. For example, being unable to group because you are in ignore lists, being booted from the flashpoint or operation before the end, valuable players leaving the group because of your behaviour leaving you unable to finish the content.
In practice, the current need / greed situation works pretty well. Everyone knows the rules, most of the time people behave decently. Your proposal adds nothing.
I agree, in the old days, players who did not abide by the social rules of a game did suffer the consequences. Ninja looters, trolls, cheaters were shunned by the community and (often) kicked from their guilds. Moreover, the stigma would stay with the offender for a long time because everyone remembered his name.
That all worked because:
a) the games were small and the communities were tight and
b) teams/guilds were essential to progress.
SWTOR has about 10000 players on each server. Loot and gear is easy to obtain in various ways. You can certainly level to 50 without ever having to group. And if you really put your mind to it, you can even have an end-game toon without teaming.
Being ignored by a few people is not a very effective deterrent, especially if you are a tank or healer. With 10K players per server, you will still find groups. The stigma of being a ninja looter, exploiter or troll might last a week at best. After that, nobody remembers your name, or what you might have done - one of the drawbacks of internet anonymity. Being kicked from a guild has even less of an effect. Guilds are not essential for progress and you could find a new within minutes if you choose to.
For all practical purposes, social consequences for bad behavior do not exist in SWTOR.
That is why I proposed a simpler, more automated loot system, especially with F2P arriving soon.
Everyone rolls "need" (or passes) and the random generator awards the loot.
Fair, equal and and without drama.