Quite honestly it's just rude and insulting. It's just one dps saying (in my mind) that they can do my job better then me. Many here have stated very good reasons why it's bad, some don't mind when a dd pulls as long as they can handle it. The bottom line is, the tanks job is to tank, the healers job is to heal, the DDs job is to do damage and the whole party's job is to work together, so let's keep it that way. If you got a suggestion for doing it different, speak up, it's not hard
But don't take it upon yourselve to decide for the party, or your gonna have a bad time