PvP

[Alram]

NPCs stay dead for five minutes at most, so it's not a "massive disruption", as you said.  Go kill a few extra mobs and come back.  I doubt you're so pressed for playing time that the absence of a quest NPC for five minutes will wreck your day/night.

Here is one example which counters your argument.
Since there is only one artisan tailor trainer it requires a special trip to Undercity in order to train new tailoring patterns.
One night some @#@% alliance warrior decided to make it his mission in life to kill the artisan tailor and kill him again every time he respawned. It was a pain in the neck. Perhaps by your definition this is not massive disruption, but I didn't like it at all. There were no high level players present to defend the Undercity.
If you think this example is a rare situation, consider the low level character who does not have the option of just taking up some other quest, but has to do his questing in the low level town being ganked by inconsiderate members of the other faction. There are not always high level players around to help.
Typically when the inconiderate alliance raiders attack an area they do not kill NPCs once and then leave; they hang around and kill the NPCs again and again.