Had a discussion with my son the other day, and I came to the conclusion that he is a hardcore gamer. And after a short deliberation we came to the conclusion that so am I.
We play WoW (and every other MMO we've tried) to excel in the game: to best ourselves and our performance: to be better each time we set our foot on the pixelated countryside. We play to be good.
You can be casual and hardcore: the hardcore is the mentality of doing your best within the frames of the game's rules. Without breaking them, mind you BG AFK'ers.
Excel yourself every time you play. That's the tank way.
The hardcore way.