People always bring this up as if it's got some huge insight into human nature but I disagree. The simple fact is that conflict engenders dynamic equilibria. It

People always bring this up as if it's got some huge insight into human nature but I disagree. The simple fact is that conflict engenders dynamic equilibria. It shifts a game from having exactly one right answer (why the original maze game got boring) into one in which you need to constantly adjust strategies in reaction to your opponent. The pattern of something positive happening to you resulting in something negative happening to someone else is one of the most prevalent mechanics in game design. Shooting is simply one of the most literal instantiations of that.