http://www.psychologytoday.com/blog/...-may-be-hiding
http://billygordon.com/2012/06/13/dr.../#.UHpbFsVX2yZ
Specifically, when we're angry our brains release the chemicals dopamine and norepinephrine. These chemicals are also released when you stub your toe and swear. They are potent pain killers and are the same chemicals that get released when you smoke crack... and we all know how non-addictive crack is.
In addition, our brains are hard wired to feel elation when "our" team wins.
In fact, this phenomenon is so prevalent that world leaders have taken note and used it:
Would that quote be less true if you knew it was from Adolf Hitler?"As a whole, and at all times, the efficiency of the truly national leader consists primarily in preventing the division of the attention of a people, and always in concentrating it on a single enemy. The more uniformly the fighting will of a people is put into action, the greater will be the magnetic force of the movement."
So, in summation, people are hard-wired into an "us vs them" mentality. Even if society weren't manipulating your "hate addiction" that mentality would still be there. There would just be no guided focus for it and there would be divisions in the closest "enemy" group (Maybe people who wear white after Labor Day?).
So it seem that, short of an alien invasion that gives us all a common target for our hate, we may be destined to fight from here until the Sun explodes.
So no one thinks I'm plagiarizing, all of this info was pulled from a Cracked article.