Establishing communication with aliens would be extremely fraught under the best of circumstances and assumptions.
I read an interesting story where there was a universal translator which "by effectively removing all barriers to communication between different races and cultures, has caused more and bloodier wars than anything else in the history of creation." Interesting angle as we I believe the default assumption is that with perfect communication comes perfect understanding.
What is spoiled? For me, the merit of a story doesn't lie in its factual details at all. I'm in it for how the story is told, not what it's about. Good storytelling is the reward I'm after, and no second-hand account of the work can convey - let alone spoil - that.
There are various reasons to experience a story. Many people wish to experience major plot twists firsthand ("unspoilt"). Re-experiencing whilst knowing the twists is a different experience.
Common scene:
Older person: Oh, you're a lad of 4 or so. Have you watched
Star Wars yet?
Child: No.
Older person: Did you know Darth Vader is Luke Skywalker's father?
Child: I do now. T_T
Ah, a reference to the hit film!