There's also a good chance that by the time a race can travel between interstellar space, they'll be mature enough not to kill everything they see.
What makes you think that? Humans just put 1 ton hover over another planet yet we still kill each other over which parts of which iron age books we think are more than just stories.
What we do know is that within a populous of a given scientific advancement its possible for there to be a massive variation of individual and group morality as well as individual education level (particularly in regards to science). We know this because it's our current world.
Based on the reality we know about it isn't terribly apparent to me that just because some population has achieved a given level of scientific advancement that some of them won't gleefully steal my lunch.
So any interstellar race is likely to be very competitive. You hope it doesn't show up as killing, but the reality is when you have two people who both want something, they fight.