So It's against the rules to need for another job?....

[Elim]

And they aren't? Once you decide to turn it in for seals or desynth, the item ceases to be for your chosen role in that dungeon. Those other people in the group may very well "need" the item for seals/desynth JUST as much as you. Again, as I said in an earlier post, I won't tell you how to roll, I'll just leave and choose not to play with you. But it is total and utter selfishness. And you'd be a fool to think otherwise.

Okay so both guy A and B want to roll on gear for seals. No problem. Both guy A and B can roll need on pieces for the class they're currently on.

Guy B isn't entitled to every single solitary piece of gear that drops in a dungeon or raid. Why? Because they can't need on every piece.