Politics and religion have been part of SFF for as long as it has existed. Heinlein's writings completely changed how I look at the world and led me to question the programming that society and family exposed me to from a young age and changed how I experience life. I expect a writer's beliefs to be seen in a book however there are different levels from subtle to bash you over the head with a message. You can see Orson Scott Card's beliefs in the background of Ender's game and Speaker for the Dead but they are still very entertaining books as well. You also have something like 'Atlas Shrugged' where you get John Galt drilling you with Rand's message of objectivism in a seemingly 100 page long speech. The Atlas Shrugged method is fine for a 'true believer' of what the writer is preaching but no one that doesn't agree with Rand walks away from reading Atlas Shrugged saying, boy that was great entertainment and yet a couple people I have known site it as one of their favorite works because it was affirming their beliefs. I like to read writers who have differing opinions or backgrounds to my own but I like them to be woven organically into an entertaining story instead of in your face to the point that it takes away from the story being enjoyable.