Humans fight for several reasons. Number one, because it is our natural instinct to fight. From the dawn of existence, humans have had to fight to live. Nature doesn't care if you want to sit down and talk it out like civilized people, it will destroy you if you don't fight against it and therefore humans have a nature that yearns to fight whenever a disagreement arises.
Second of all, next to nothing can be completely resolved peacefully. In negotiations, when people do decide to be civil about it, some one will always come out as the loser, in that either they won't get what they want exactly or they get totally screwed. And face it, if you want something, sure you can tell yourself to suck it up, but that's not going to change the fact that you want it and you can't have it.
Finally, humans like to fight. It's our natural competitive spirit brought out. It lets you know who is stronger and who is not, be that through physical confrontation or some other form. The bottom line is that we want to be better than others and if you don't think that you're lying to yourself.
And as a side note, I don't mean to be disrespectful, but when you bring up an argument like this could you please use proper grammar and spelling.