Art can be used in many ways. It can inspire, for certain, and I always love for art to inspire me, but it can also caution us.
1984 and Brave New World, for example, caution us against too much reliance upon government to do what is best for us.
Lolita, likewise, cautions us not to be so sympathetic and understanding of a person that we end up condoning what they do without judgment.
I think in 10 to 15 years, Lolita will be banned on college campuses again. This time not because it describes the mind set and behaviors of a predator, but because it contains the condemnation of the reader in finding sympathy for the predator.
You are supposed to be disgusted by Humbert, and should be. And yet his arguments for how he abuses Lolita, that he truly loves her and it is just the way he is, are the arguments that modern liberals use to excuse all of their depravity.
When you catch yourself smiling at descriptions or clever passages written by this man (the novel is in first person), you suddenly remember that he is an awful and miserably immoral monster.
That is the cautionary tale of Lolita. Very charming, smart, caring people can be absolute demons in human form. And we need to remember that.
For my money, that is what people need to be cautioned against.
Nabokov is a writer who has always been studiously avoided by Academia. He does not fit into to any of the fashionable categories that Lit Departments cater to these days. His politics were decidedly conservative (staunchly anti-Communist, defended Joe McCarthy and the Vietnam war) and many of his comments would ruffle P.C. feathers today (about pandering to race/gender based standards etc...)