If you're space faring on a large scale you probably had to leave conflict and infighting to lesser races, just so you could focus energies on making that leap.
IMHO.
That's just another argument that humans are truly a race of barbarians.
relative to what? we don't know how violent alien species are. they could be very peaceful in comparison, but it is just as likely that they are more violent than we are.
All the evidence available to us (Earth) suggests that the best killer on the planet will be the dominant species. It's been that way for billions of years.
The video argues many points, an important one are
1 you can't stay hidden, advanced civilizations will detect you or can send probes to destroy any viable solar system,
2 if you try to kill everyone else you will eventually find someone bigger then you so maybe the strategy to make alliances is better, you will have a better chance surviving in an alliance when you eventually meet something bigger then you.
Since I realized that, I've stopped whatever slight worry I may have had about the "kill everyone you discover" theory. If it was going to happen, it wouldn't happen in the near future because some of our radio waves finally got somewhere, it would happen eight or nine hundred million years ago and we wouldn't be having this conversation at all.