Just think of all the ways that the game is improved when people multibox.
Please note that I am using the same definition as
@StevenSharif . Multiboxing is 1 person using multiple separate computers and peripherals. You cannot cause multiple actions or actions across multiple accounts with a single key press or mouse click (that is botting and can get you banned).
Intrepid gets the extra income so that they can employ more developers to make the game even more amazing!
More characters mean that the game economy is boosted so that more characters get more money (since the multiboxers would purchase more equipment as they only have so much time).
Groups have a greater pool of characters to draw upon since more characters created gives wider selection.
Guilds can be more focused on their people as they know that the multiboxers have a good selection of characters. Easier to get a specific set of characters together to do something.
Raids would be easier as people would have more characters to choose from. And have a better chance of the exact composition they need.
Nodes would be more affluent as more taxes would be received from the extra characters.
PVPers and Gankers get extra targets that will be easier to kill.
So the whole game is better even though the person running the multiple computers loses out as they don't have enough time to focus on 1 character and level it as quickly as other people. And they have to pay more real money as well as extra in game money for taxes.
So let's give a cheer to the (legitimate and not botting) multiboxer who makes the game a better place!
Edit: Sorry for the wall of text.