Is making your whole story dark and making the ending happy considered something hated by readers?

The ending that I always had in my mind was dark, but now I have another idea, a happy ending, and I feel that it is satisfactory to me.

Is it considered something hated and bad writing?

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I think my problem is that my main character doesn't deserve to have a happy ending. I may sympathize with what happened to him, but everything he does makes him not deserve a happy ending. I'm contradictory.I see him as unjust and oppressed, and I don't know if a person like this deserves to be happy or at least die.Let him rest in peace, or let him rot in hell.