No. Why should I be forced to tank or heal if I don't want to or lack the skill to do so?
You should be encouraged (not you personally but "you" as the player base) to take up a healing/tank role. If you queue as a DPS and you're other specs cover those two needed roles the game should offer try and find a way to get you to do those roles. Not entirely sure HOW they could do it maybe something like if you go in as a tank your VP limit for the week gets increased by 250 same for a healer. Sure it might be open to abuse but then players will kick a healer whos a dps in disguise!