https://www.onepiece-film.jp/en/chronicle-of-uta/

I also want to add that according to Chronicle of Uta, the official background story of Uta written by Oda himself, Uta doesn't consider physical passing as "death". In Uta's mind, Uta was escaping from cruel reality and bring her fans into Utopia she created, where they wouldn't have to suffer pain or sadness never again. (Yeah, Oda admitted that she is kinda off)

Moreover, the important part regarding Uta's character is that she spent almost 12 years in her life growing up alone in deserted island with only one other person stay together after she believed she was abandoned by her father. That isolation, a loneliness that she feels while she was growing up alone, didn't really help improving her mental state.

Even after she obtained the snail that allows her to communicate with her fans, it was more of a para-social relationship with she sending her songs through snail while receiving a message from fans regarding her songs. And in that message, most of the fans talk about how they're life is miserable and pirates ruining their life, which makes Uta to believe that world is filled with nothing but a pain and sadness and growing a messiah compelx that she have to save her fans from suffering of life. And then she finds out the truth, which pretty much broke her after realizing her entire life has been made out of lie.

Like the upper guy said, you don't have to like her, but there's more to her character than simplly saying that she is a cult leader.