This sci-fi counterculture novel espouses libertarian philosophies including free love and, more generally, the idea that morality is whatever the individual wants it to be. The main character, Martian-raised human Valentine Michael Smith, claims "Thou art God!"
I read this at, if I recall, age fourteen. I didn't understand much of the ideas therein until much later, so fortunately, they didn't influence me. However, the book was an example of how when I was young, I'd say that I loved a book because it was too deep for me to figure out. For some time afterward, I called Stranger one of the best novels I'd ever read. It's not on my radar now. I am not God.
(FYI: Supposedly, the character Jubal Harshaw represents Robert Heinlein.)