I only need look at the title of the forum and to recall when this was new to know that the origins of dual boxing came long before the multiboxing we know today. It addressed a very specific niche for very few players. Players who were not challenged by playing a single character had the option of playing two. Then it went up to a party and ballooned out of control to what we see today.
I view this as a perversion. It reaches a point where the challenge is lost and it can only represent the ultimate form of griefing. Think about it this way. What is the impetus to buy a few more accounts whenever someone trounces us in world PvP? To win the next time, right? Lets forget about getting better on what you have. That is the sticking point for me. It moves away from actually learning how to play two characters and moves into a numbers game. Just add 20 more accounts with the same one button rotation and justify the cost by going around the world looking for a fight.
Why not do arenas? Why not try out challenge modes? The answer is they aren't actually looking for a challenge. They are looking for bragging rights to something that isn't even worth bragging about. A giant waste of time and money.