Contrarily, I think that any civilization capable of reaching Earth must also exhibit the most humane (aliene?) characteristics such as love for justice and respect for other lives. I'd imagine with their great power, every individual in their planet can, with the flick of a finger, wipe out a large portion of their own race if not entirely. They must have learned to coexist or face self destruction. It's a prerequisite to freely roam the universe.
What about killing for their own survival, after all respect for the lives of one's own race doesn't translate to respect for lives of others. This may be true, but with their intelligence I'd think they're smart and reasonable enough to explore other possibilities. I don't think aliens in soon-to-be-out-of-resources ships desperately flying around the universe for energy is a scenario advanced intelligent life forms planned for. It's more likely that they accept a peaceful conclusion to their existence.
Of course, it's very possible that we're all wrong since we're projecting our own primitive reasoning on species that are a lot more evolved.