Would you really want to be around your own kid when they're all grown up if they keep resolving disagreements by brute force?
The use of brute force is always a choice, in any event.
Every time you engage with others, you are free to consciously choose whether you want to engage in pro-social behavior or even if you want to consider the other person as someone who is real.
Nothing ever stops anyone from choosing to believe that they are the only real thing in existence and that everything else is shadow.
"Solipsism (i/ˈsɒlɨpsɪzəm/) is the philosophical idea that only one's own mind is sure to exist. The term comes from the Latin solus (alone) and ipse (self). Solipsism as an epistemological position holds that knowledge of anything outside one's own mind is unsure. The external world and other minds cannot be known, and might not exist outside the mind.
As a metaphysical position, solipsism goes further to the conclusion that the world and other minds do not exist. As such it is the only epistemological position that, by its own postulate, is both irrefutable and yet indefensible in the same manner."
http://en.wikipedia.org/wiki/Solipsism
