I'm guessing you don't like the philosophy he is being exposed to. Is he a good person? Is he doing what he's suppose to? School, work, his chores? Is he following your home rules? If yes, you're doing your job. If he is not it is your responsibility, as a parent, 'to move his mind in a different direction'.
You have to know the core beliefs of a philosophy to be able to argue your point in the constraints of it.
Young people, with little life experience tend to rush to the extreem of a new philosophy. So, 'Preach moderation'.
The way you can influence the way he thinks is by your actions. Believe me, he's watching. When he does something that is living his philosophy that you don't agree with, ask him to explain how it fits in his philosophy. Explain how it doesn't fit in yours or possibly real life. Listen, engage, ask questions. Try to understand his point of view. Dont judge.
He's young. Point out he more schools, yours included, he's exposed to the more rounded he will be