The beautiful thing about fiction is that it can predict how reality will go before reality happens. It can hold up a temporal mirror to society and say to it "if you don't stop what you are doing, this is what will happen".
If we were to rely on non-fiction to teach people all the time then we would only be able to react to problems instead of act to avert them because with reality we can only learn in hindsight.
Fiction can be used to show what will happen if a certain behavior continues or is started thereby convincing people to either continue or stop. Fiction is therefore very useful in convincing people of certain ideas.
