I just completed a Tam-Tara Deepcroft run with a tank who was completely unwilling to learn to tank properly. This player basically acted like a angry toddler and said "you're just criticizing me" in response to "You need to use flash 2 or 3 times to establish a base aggro then use your main combo to keep aggro"

Players like this should not be allowed to continue accessing DF to be a burden on other players. When reported, GMs should have a policy to flag this person so they have to complete all Hall of Novice duties before being allowed to return to DF play.

A GM basically told me that if a player wants to play terribly in a DF then they are allowed to do so and other players aren't allowed to tell them how to play properly.

This sort of policy writing is just irrational and detrimental to all players. It basically say someone can harass other players in the DF by playing poorly. SE really needs to revise their policies.