When it comes to DPS, you have an advantage over healers/tanks because you can practice rotation mechanics on dummies. Sure, in theory healer/tank could in a sense but the fact of the matter is using a parser can help you make a rotation that is easy/manageable for YOU. At the same time it allows you to optimize your damage.
Like Alkimi said above healers/tanks get called bad all the time, but call a DPS real bad and suddenly the world is ending. If we can't hold DPS to the good/bad standards we place on healers/tanks then no one holds the right to complain about bad healers and tanks.
P.S. It doesn't take an elitist douche to use a parser. A parser is there for self/group improvement; the better you and your team are the more likely you can carry friends who aren't as good at the game. Simple as that.