because you mentally turned yourself off after seeing moral/philosophical points that you disagree with. It's okay, this happens.
I know some people who are quite intelligent and big SF fans who never got why Dune is so popular. Precisely for the same reason.
Personally, I hated the movie District 9. I thought it was very shallow, just a not-so-subtle vehicle for the writer/director to push his leftist views. Super intelligent alien beings that have interstellar spaceships and artificial gravity, and yet act like idiots? Really? Aside from their high-tech stuff, their behavior is exactly like that of prison inmates with an IQ of around 80. Ruins the story for me, the whole time I was watching it I was thinking, "Why don't these aliens just do _____?"
However in retrospect, it is possible that District 9 is not entirely worthless, it may contain some good parts that I overlooked due to my disagreement with the parts that were stupid.
Stranger in a Strange Land on the other hand is a masterpiece -- a towering achievement that stands out even among the greats of science fiction -- because it's so original.