I've found that pretty much any novel that tries to beat the audience over the head with a political or social message rather than tell a story fails as a work of literature. You wind up with cardboard cut-out characters, stilted dialog, and far-fetched plots rather than anything interesting or believable. This is usually true whether I agree with the political/social message or not.
The only exceptions to this rule are explicitly works of satire or parables, e.g. Huxley's Brave New World, Orwell's 1984 and Animal Farm, etc.