Since the eradication of clan diplomacy, all clans are now effectively "at war" with every other clan.
Gone is clan score (which was infinite), and replaced with energy (which is a finite resource, generated hourly with the hourly sum determined by your EPH (number from 0 - 60))
Like pothead stated, due to the nature of the game, where all clans are warred and with energy being finite, you have to supplement your energy with other means.
This generally has come to be by (as pothead stated) creating what is referred to as a "freaked" build (think perfect build on steroids), and then creating a horde of bots at the min level that can attack your "main perfect build". Thus the term dumper, as you are dumping energy from lower level bot onto your main.
I thought the purpose of bots4 was to irradicate the bot fighting? or was this originally the plan and then it got circumvented?
As far as this goes, I'm assuming you meant getting rid of whores, rather than bot fighting, as that was the original plan for both game designers. Think "real wars," but as the world works, people always gravitate towards the path of least resistance, thus dumpers were created.