The book is fine. It does not at all empathize with the pedophile, it doesn't sexualize Lolita. Stanley Kubrick's film adaptation however, is totally fucked up. The book is about a fucked up subject for sure, but it absolutely condemns it.
From what I understand, while the book is told from the perspective of the pedophile, who is proven to be lying or wildly distorting things in a brief moment when the victim gets to speak, the movie mostly plays it straight, with the child seducing a grown-ass man.
The problem isn't the book inherently, but the inevitable reception when put in the hands of pedophilic cultures like those of the anglosphere. Nabakov was adamant, for example, that the cover should not depict Lolita (the character) in any literal sense (or any person, iirc), for obvious and correct reasons. You can look up what cover art has nonetheless been used if you are feeling masochistic.