Because films’ promotions may deliberately conceal information about tragic events in the story to achieve maximum impact and nobody thinks that is unethical.
This feels a lot like talking to Eliza. Your replies very vaguely connect to what’s being discussed in this thread, but there’s just no substance or coherency to the argument.
"When a film makes you sad you are aware of what's going on" is your claim, but I don't see how that applies to something like, say, Terminator 2, whose entire goal, according to Cameron, was "making the audience cry for the Terminator," yet was not promoted as a sad film. It's hard to come up with a principled difference here.
The Terminator 2 audience knows the film is an authored fictional story. It can make someone cry when they didn’t expect it, but they understand that the filmmakers are intentionally trying to provoke certain emotions. If you can’t see the myriad principled differences between that situation, and logging onto Facebook expecting to see an unfiltered selection of posts, I really can’t believe you are trying hard.