I believe the "know your role" really needs to apply to people who queue as dps then try to tank. I would almost say this is where Bioware should take a page from WoW's book and allow double speccing.
Yes, this issue seems to come up alot. People saying 'Well, I am in my tank gear but DPS spec'd'. Then queue as a DPS or respec to full Tank. Currently you can't tank and dps all-in-one and be 100% successful. Which is the way it should be. Either tank or dps. Just pick one. It isn't that hard.