Tanks: Your main job is to keep aggro and maintain it. If you wanna push some more DPS out, more power to ya, just don't get too fancy and lose aggro.
Healer: Your main job is keeping your party alive. If everyone's okay on health, and you wanna push out some more DPS, more power to ya. Just don't let anyone die when you're too busy DPS'ing in Cleric Stance.
DPS: You have ONE job.
As long as you are fulfilling your main role, whether that be keeping aggro or keeping everyone healed, I really don't care if you wanna push out some DPS, just don't wipe the group because you forgot your main role.