I would fall into the hard core pvp gamer as well. having played a pile of fps games and many other types of pvp games as well.
in context of WoW one simple reason for ganking lowbies is that they are on the other team.
like in pretty much any war you dont base your choices on killing the other guys based on how much of a badass they are but on the fact that they wear the other uniform.
while killing lowbies isnt really my cup of tea I have done it many times under many circumstances. One of my favorite things to do when I played WoW was to sneak my 65 horde rogue into an ally town and kill whatever allies I could. the challenge in this case is not dying to the guards who were largely immune to my rogues escape capabilities. getting into an ally town killing 6 ally players and not dying causes a crap ton of chaos for the other team and quite frankly cracks me up when I get away with it.
one of my other favorite things to do in WoW was when I had a few RL friends, there were 4-5 rogues and one warlock who we affectionately called “Bait” we loved it when some high lvl ally would see the bait and move in to attack the closest rogue would stun and start the attack then the other rogues would move in and stun as they arrived. most players were dead before they ever became unstunned. we would kill some really high level toons this way and yeah some times they would kill a few of us in the process but that is why you play the game, to lay the ambush, to lead the charge, to overrun the enemy. beating the games ai is a joke.
regarding the anonymity part I played on an EQ server where you only had one toon, you werent known for who you were in real life but you had no alts to play if you were a big enough douche to piss the other teams off to they point that they hunted you. even on this server there were a few jackasses, most of them fell into the category of true griefers. using out of game software to cheat. they were the ones most likely to end up banned.
also instead of thinking of it as a pvp server try thinking of it as a Competitive server. in any competitive environment humans will lie, steal, cheat, and do whatever it takes to get ahead. its foolish to think otherwise in the face of pretty much all of human history. so in any team based environment its pretty much expected. people who dont expect this behavior (imho) are the ones who arent seeing things clearly. killing lowbies from the other side is a dick move but its also a dick move that again humans have done throughout history, killing your competitors for food/water/women/territory/whatever has been s.o.p. humans are the only species who really understands that those people living over there will one day want what we have over here and we should probably kill or drive them off now while they are weak and we are strong because in the future they could be the strong ones.
(no I am not saying this is the actual thought process, but somewhere buried in our primitive brains those ideas are rolling around)
so when players come from a pve mindset (or a Co-operative mindset) they are used to helping each other out, giving a hand up and in general being cool dudes.
in the real world I hate the competitive obsession Americans have over everything and anything. its destructive at a level that is strangling every aspect of life from the economy to education.
in the game world? gimme some fool who I can shoot in the face every single time.
(I do have a soft spot for Minecraft, but I cant wait for stable multiplayer servers)