It's not selfish to roll for stuff you want.

There's no reason for tanks or healers to always greed and give up their perks. Tanks and healers are in high demand. Even with the small perk of not rolling against another tank or healer in 4 person content, they are in high demand.

If you think tanks and healers have a great deal because they get a couple extra pieces of gear now and then, then the solution is simple: play as a tank or healer. If that isn't enough to motivate you to change from dps, then you've realized it isn't a big deal and your argument is invalid. If it does motivate you, then great. When you feel like getting a couple pieces of extra gear, help out with the tank and healer shortage.

It's selfish to ask people to give up their perks, when it's so easy to instead change roles and help out if you want those perks.