When meeting alien civilizations we will be encountering cultures that developed entirely without any contact with us.

Let's say we encountered an alien race and they seemed almost exactly like us. Human rights, free speech, free press, democracy,...

But then they consider personhood to start 6 months after birth and even have restaurants that serve newborn babies.

Or maybe a civilization where bestiality or necrophilia is common even a traditional practice in their society? Maybe people consider necrophilia to be a way of "honoring the dead".

Or what if we run into pedophilic aliens?

How do we respond to that? Do we accept them, do we try to change them? If we try to change them do we gently nudge them or go to war? Do we just avoid them?

And what if they have a whole wealth of technology and resources we could benefit from if we decide to just let it go?

And then what if they don't?
But how would we go about applying morality to species completely foreign to this world? Assume we somehow come into contact with a sapient species that is say... completely hive-minded for their survival or something. Compliance, submission, and participation are absolutely necessary not only for the survival of their society, but for their species as a whole.

Freedom is not tolerated. Those who would say otherwise are mentally ill, and are to be put to death for the greater good of the species.

For species completely foreign to this planet, they have developed in vastly different ways. How would it be possible to apply our morality when our societies intermingle? And when there is no possible way to prevent conflict and war after the initial contact, who is right?

I'm interested to see what ideas you can think of