I pretty much only play a healer or support character in MMOs. If a game has no healing (some KMMOs that have come out lately) or the healing role is unsatisfactory to me for some reason (FFXIV, Wildstar to some extent), my interest in the game dies pretty fast. BF, on the other hand, loves all three roles of the trinity and is proficient at all three. Whatever he "mains" in an MMO usually boils down to either a.) what his raid or core group "needs" when the group is first forming, or b.) whichever class has the playstyle that he enjoys the most. He was a SCH in XIV and is a Demon Hunter main in WoW (he's addicted to their double jump and glide, lol).

Meanwhile, my old raid DRG only plays Protection Paladin (a tank) in WoW, and our FC leader is a tank for life and will only play MMOs with adequate sword-n-board heavy mitigation-based tanks. He fell out of XIV when the adjustments to PLD were always on the DPS end, and not the mitigation end, because the content was so oriented around it that he "didn't feel like a paladin anymore while playing". This was when we raided Savage Gordias.

I don't ever assume that people who like DPS are responsibility-shirking mouth-breathers. There's a lot of tanks and healers who do, maybe, but I'm not one of them. Sometimes it just boils down to liking the big numbers exploding on the screen, or just liking the gameplay/spell effects/gear appearances of another class more. Don't let it worry you too much, OP.