I think it goes a lot deeper than this.
There is very little that is more thrilling and cathartic than ganking another player. Especially when you know that you've completely ruined their day and possibly made them ragequit the game entirely. There's usually a bit of guilt that tinges that thrill, which just makes it all the sweeter.
There's also very little that is more thrilling and cathartic than narrowly escaping ganking, either by means of killing the ganker first, clever mechanics use, calling in your friends or the city brute squad, fleeing to town, or even just hiding and waiting for the ganker to go away. It means the "bad guy" loses and the "good guy" (you) wins.
On the flip side, there is very little that is worse than being ganked by another player, who kills you for no reason other than they can. Some people suck it up and chalk it up as a learning experience, but others become enraged and all too often they do stop playing in anger and disgust.
In both cases, ganking (or being ganked by) another real human being can be, by far, one of the best and/or worse experiences in online gaming. There's just something about it that amplifies emotions ten thousand fold, where the exact same thing done by a brainless NPC is forgettable within an hour but we often remember a particular ganking years and years later. The stakes are just so much higher for some reason.
The ideal environment for a ganker is one where ganking is allowed, few other people gank, and many many people are around for other reasons. I believe this is why free-for-all PvP servers of any MMO tend to have much lower populations than regular servers. Everyone wants to be the ganker, but no one wants to be the gankee. PvP servers start out full of people wanting to be gankers, but no innocent population to prey on. Eventually, the bastards leave the PvP servers and try to figure out ways to gank people on normal servers, or go to different MMOs with a better balance between ganker and gankee.
MMO Companies have tried to deal with this aspect of online gaming in various ways, ever since the days of MUDs. Some ways are quite a lot more effective in others. A free-for-all like the writer wants is very dangerous, because you get people angrily quitting and eventually the place is a ghost town. Some smaller MMOs and MUDs have "regulated PvP" where players can complain to mommy if they got killed "inappropriately", but that takes a lot of resources to do. I'm personally a fan of having separate "sides" and free-for-all PvP zones where it's kosher to stomp on each others' faces and hunt them down but you can still do normal quests and the like. Entirely PvE MMOs like most of Everquest 2 can be nice, but even then there's still some ganking.
One thing I am very glad most MMOs have gotten rid of is the "lose all your stuff" mechanics. Getting ganked in PvP is painful enough without it.