Hello,
First of all, I usually only use need in Ops for rare mats that are used in crafting, BUT:
1. please consider that each member of an ops team is actually entitled to roll by their own needs and by what they consider THEY need. They all spend their time for that Ops, so, they all are equally entitled to roll. Also, is a game of chance so, no one can restrict someone to roll for one or more items. As for saying that a well geared toon is not entitled to roll over lower gear items, think again; if they are well geared then is most likely that their contribution for that Ops success to be equally bigger .... so ... who's more entitled?
2. using Master Loot in Ops should be announced from start, so that those that are uncomfortable with it may not participate at that Ops.
3. I've heard of the expression "but the player X needed that item more"; very well ... let everyone roll and then let the one that need an item more to discuss with the winner to get that item, if they really need it so bad. Is a free economy, not communism.
4. If you see someone doing "ninja rolls" no one stops you to do the same, especially if otherwise was agreed in the Ops start. And if you will win something you need, decide who's needing it more and give it to them.
Again, over-regulating this sound a bit like communism, where there are others to decide whether or not you need anything. (and before you cry out, I lived in such an economy for almost 20 years and is not cool at all)
All the best,
Iskara
PS: I'm speaking of PUG runs, not guild runs, in guild runs, every guild is entitled to have its own rule about looting, and probably that's why the Master Loot is there for.