...by virtue of them being able to traverse the black of space and visit other worlds, they overcame themselves one way or another and may actually be benevolent beings.
Or maybe they were the strongest and most ruthless among the varied intelligent subspecies on their planet. Maybe they achieved unity of purpose by eliminating the others, not by learning to get along with them. Assuming Nazi Germany and Imperial Japan had been victorious in WWII, it's likely that sooner or later they would have turned on one another and only one would have survived. That one, then, would be who represented Earth in eventual interstellar contacts. Expansionism and domination were the goals of each, and there's no reason to assume those goals would have changed once it became possible to expand to other planets and dominate other species.
Bear in mind, Blast, that I'm not saying this is the case. Simply that my scenario has just as good a chance of being accurate as yours. The intellectual elite like to assume that peace, reason, and cooperation will always prevail, but the fact is that we are on the brink of interstellar travel (probably 200 years away or less) and the "I want what he has and I'll take it by force, if necessary" mindset that leads to war has not diminished significantly from mankind since the first humanoid struck down his neighbor for a scrap of food rather than find his own.
I hope you're right, especially if they get here before we get there. I am optimistic. But I will not be blinded by my optimism.