The removal of town guards from all wow powerleveling towns except for major cities(ex: Orgrimmar, Stormwind) on PVP servers would fascilitate a much more hardcore game experience much like it was when the game was first released.

People roll on PVP servers because they want to kill the other faction, the inclusion of town guards is an interferance with this game mechanic. If people don't like being killed because there are no guards, they can go roll on a PVE server. As it is town guards do little to deter people from assaulting towns, other than stopping them from controlling the town until they get bored. There is no problem with this, people would go to towns to oust the opposing faction.

PVP servers are supposed to be harder than PVE servers, with town guards the only real wow powerleveling difference is being randomly killed when you're not near a town.

There's also the issue of people exploiting guards/exploiting guard mechanics:

Rooftop camping in Northrend, and Outlands in neutral towns so that they can shoot/cast spells at people on the ground without fear of retribution from the guards or other players(if someone is shooting you, and you retaliate the guards kill you not them.

This does not mean you should give the guards knockback, I would rather see the wow powerleveling complete removal of guards, this would allow people to retalitate without fear of the guards mistaking their actions as offensive rather than defensive. I'm sure a lot of people feel the same way.