It's a bit of an intrinsic problem with the game mechanics as such vs players coming from other games where a healer heals, a tank tanks and DDs do damage.
I feel comfortable with dealing damage as WHM, but others might not and personally, I don't care either way. When I'm the tank and the healer just heals, fine with me. It's not like my Pally would contribute enormous DPS either and I'm busy enough already to even notice.