So you think it is completely, fair, sensible, and reasonable that a tank should be nigh-defenseless against every dps or healer class/spec?
On a PvP server, I can't even imagine trying to complete a single quest as a tank. There must just be a line of HK-hungry dps just waiting their turn for you to rez. What chance do you possibly have with no offense, a completely worthless defense, and no reactive damage to at least make you dangerous to a melee dps?
Tanks aren't defenseless. If you get jumped questing by someone ready to pop everything, you do what every person does - escape, kill or die trying one the former.
Again, have you actually bothered trying to PvP or are you just flailing about because you got ganked once and have no idea what other classes even do now?
Since when did you go around caring about PvP anyway?