The idea that "any society sufficiently advanced enough to travel through space will also be advanced enough to avoid violence," is a very old one. It pops up in the words of scientists in '50s movies all the time, usually just before they try to make peaceful contact with the advanced aliens and are destroyed by them. See for example The Thing From Another World, in which the scientist Carrington makes almost that exact argument.

__________________
"You miss 100% of the shots you don't take" - Wayne Gretzky