You are worried that, given your assumptions, civilizations might not be willing to pay an extremely high price to do things that aliens would like if they knew about them, which they don’t.
But one of your assumptions is that every civilization has a moral system that advocates attacking and enslaving everyone they meet who thinks differently from them.
It would be worrying if a slightly bad assumption led to a very bad conclusion, but a very bad assumption leading to a slightly bad conclusion doesn’t strike me as particularly problematic.
You are worried that, given your assumptions, civilizations might not be willing to pay an extremely high price to do things that aliens would like if they knew about them, which they don’t.
But one of your assumptions is that every civilization has a moral system that advocates attacking and enslaving everyone they meet who thinks differently from them.
It would be worrying if a slightly bad assumption led to a very bad conclusion, but a very bad assumption leading to a slightly bad conclusion doesn’t strike me as particularly problematic.