Whether an act is "evil" is a theological question, so to the extent plaintiffs are actually relying on the word "evil", separation of church and state will prevent the court from even considering their claims.
[Most?] atheists have moral codes. Yours is not necessarily mine. Sorry to be pedantic, but implications of atheist unity really bug me.
The aliens observing our supposed primitiveness are just the ones that came out on top in their latest civil war and went out exploring using the technology that the 14,000 years of war cultivated.
Maybe they're the most obnoxious, spoiled, entitled assholes you could ever imagine. Luck rolled their way ten thousand times in a row and they act like it.
There's absolutely no good reason to default to believing aliens are likely to be far more enlightened than we are.
There's no good reason to imagine some civilisation has figured out how to cross the vast interstellar distances and then pop in to see us during their lifetime.
Since we are already in the realm of pure fantasy, it doesn't alter the argument's validity to also assume these magical creatures are enlightened.
If you go back a couple hundred years and talk to the people then I imagine you could achieve a similar effect. They were just as certain they were correct as we are, and they are just as wrong.
Whether challenging an act is within the reasonable scope of a contractual obligation to report suspected evil is, however, not a theological question, and does not involve deciding the question of whether the act is, in fact, evil, whether or not that is a theological question (it is not, necessarily, it is a moral question.)