We fight because it's the best way to prove who's right.
It makes the winner look stronger
We fight to protect people
We fight because it's human nature.
As much as modern fighting is fairly pointless, in the past fighting has advanced the progression of civilization. Without fighting, the strongest guy would take over everything, uninterupted.
Unfortunately, there is no justification for fighting today, it's all a big dick waving contest. A contest where alot of innocent people are dying in the process. OK, that's enough of my hippy, sentimental side.