How the game must be played:

Healer heals, Dps does damage, Tank protects the party.

How elitists and pseudo elitist want EVERYONE to play the game:

Healer DPS and sometimes heals, focus on DPS at all times, damage dealer, its ok, do anything you want just be sure to blame the healer for any wipe, Tanks protect the party and most importanlty do DPS, NEVER be in tank stance always dps stance.

FF XIV in a nutshell.