Vladimir Nabokov and his novel Lolita have received significant criticism, primarily due to the controversial subject matter and its depiction of pedophilia. Some of the key criticisms include:

1. Morality and Ethics: One major critique revolves around the portrayal of the protagonist's attraction to an underage girl. Critics argue that the novel's subject matter can be seen as promoting or normalizing pedophilia, leading to ethical concerns.

2. Perversion and Obsession: Nabokov's exploration of the darker aspects of human nature and the obsession of the main character have drawn criticism for delving into disturbing and taboo subject matter.

3. Exploitation and Power Dynamics Critics argue that the power imbalance between the adult protagonist and the underage character depicted in the novel issues of manipulation, exploitation, and abuse of authority.

4. Appropriateness: Due to the explicit nature of the novel's content, some critics question its artistic value and argue that the explicit scenes and language serve no legitimate literary purpose.

5. Cultural and Contextual Factors: The novel was especially controversial during its initial publication in the1950s, when discussions about such sensitive topics were not as open as they are today. Some viewed the novel as offensive and inappropriate for public consumption.

Despite these criticisms and controversies, it is worth noting that Lolita has also been praised for its literary merits, including Nabokov's innovative writing style, complex narrative structure, and wordplay. The novel is often considered a significant work of modern literature, provoking discussions on artistic freedom, censorship, and the boundaries of literature.

"Lolita" by Vladimir Nabokov has faced varying degrees of censorship and attempts at being banned in different countries and time periods. Some of the main reasons why "Lolita" has been the subject of bans and challenges are:

1. Sexual Content: The novel delves the sensitive and controversial theme of pedophilia, as it portrays the taboo relationship between a middle-aged man and an underage girl. The explicit nature of some scenes and the language used in the book have led to concerns about the potential harm it may cause or its morally objectionable content.

2. Obscenity and Offense: Due to its explicit depictions and subject matter, "Lolita" has been perceived as offensive and obscene by some readers and communities. The book's content challenges societal norms and pushes the boundaries of acceptability, which has led to objections and bans in certain areas.

3. Moral and Ethical Concerns: "Lolita" has been heavily criticized for its portrayal of a pedophilic relationship and the potential normalization or romanticization of such behavior. Some readers and critics argue that the novel's content is morally objectionable and goes against ethical standards.

4. Protecting Minors: Concerns about the potential impact on young readers have been raised, with some arguing that the explicit content and subject matter of "Lolita" could be harmful or inappropriate for young audiences. Ban attempts have often been motivated by the desire to shield minors from exposure to this content.

5. Cultural Sensitivities: The novel has faced bans in some cultures or countries because it challenges societal norms, cultural values, or religious beliefs. The explicit exploration of taboo subjects may clash with local sensibilities and result in banning attempts.

It's important to note that while "Lolita" has faced bans and challenges, it has also been widely praised as a significant literary work for its artistic merits and exploration of complex themes. The banning of a book is often a reflection of differing opinions on acceptable content and the limits of artistic freedom.