Imperius said:
Peace is a lie, there is only passion...
Hatred is a necessary part of human existence. With no natural predators and now that we have modern medicine, who and what will keep the population in check? The answer: War.
It's natural selection on a massive scale, and it is far easier to kill a man when you hate him.
Or at least, I would imagine so.
Edit: Yes it's sad, its destructive, it destroys lives and all the rest, but let me ask you: what would happen if there were 5 men, and only one chicken left in the world?
They'd have an Orgy? The chickens invited too.
@cameron112497
Hate is a mechanism we humans have in order to lower our inhibitions towards violence. While that may seem wrong at first glance, it is actually for self defence (and by extension, protecting the tribe). When someone or something becomes a threat to you or those you care about, hate is an involuntary response (unless you had a prior relationship to the instigator). It removes "safeguards" in our mind and allows us to act in a situation of potential danger.
Of course, the majority of people are far removed from the need for such a basic and primal reaction. That doesn't change how we are. We are still primal at the core, but we can temper these drives through will and discipline.
The problem with hate is that it doesn't discriminate between a potential threat and a perceived threat. How this is a problem is simple... there is a very low threshold for something to be "perceived" as a threat. A person who does better then you at something can be a "perceived" threat to you, even if they would never endanger you. A person who owns more then you (greed) or owns less then you (desperation) can be perceived as a threat.
As an example of a day to day misuse of hate, employees hating their employer (or students hating their teacher). Not saying hate is unjustified in these cases, the employer could be corrupt, or the teacher could be an asshole. However they are highly unlikely to be a physical threat. So where does the hate come from? Fear of their power over you. An Employer has the ability to fire you (though not without provocation) and the teacher has the ability to punish you (again, not without provocation). They may not ever act on it, unless you make them, but the simple notion that they CAN do this makes it a perceived threat to us (though not necessarily a potential threat).
Most people don't express hate towards a person in power as the may have rationalised the perceived threat and in turn diminished their hatred towards the instigator while others might not do this internal filtering and not realise they aren't in any danger (and not acting rationally).
For most scenarios where hate is the source of some grievance, I can use this analyses to break down the reason for it. Sometimes it's not as direct as the above example, like in situations with bullies, who are projecting their hate towards another person though that person may not be the source of it. But by and large I find this take on it to be a pretty reliable method of analyses (though not infallible).
EDIT: Note this is an observation on my part. Not fact. It is a hypothesis I have worked out though haven't put any effort into proving (or checking to see if anyone else has explored it). It works more often then not but it isn't perfect.