My answer, as it usually does, comes down to story. If the story is engaging and compelling, readers are willing to forgive a certain amount of inaccuracies and illogical assumptions. It’s tricky, though. It doesn’t matter how great a story is; at a certain point the weight of “unreality” will crush it.
I agree! But let me expand. I think there’s two important times when it’s fine for a story to be unrealistic.
One- When you’re making crap up. Magic isn’t real–there are no dragons or fae or sparkly vampires, and you can mutter charms all you wish but your neighbor’s dog won’t stop pooping in your lawn. But you can write about these things in fantasy and its fine. That unrealism is baked in, it’s a fundamental part of the story. Same thing goes for time travel and faster-than-light in science fiction. They make the story work, and the reader doesn’t care about Einstein’s judgmental glare.
Two- When it’s important for the drama. Most people will acknowledge that things like science, forensic investigation, and computer cracking are long, tedious processes mostly done in brightly lit fluorescent rooms by average looking people who drink too much caffeine. People who almost never engage in witty, flirty banter. When these things come up in stories though, reality gets ignored and everyone pretty much accepts it. Why? Because reality is BORING. Science should be done in dark labs, lit only by snazzy glass touch screens. And all lab techs should be hotties who can spin dialogue like DJ’s of snark. It’s unreal, but we’ve all decided to pretend it’s really that way, because fun.
This is where Hunger Games falls for me. Is the books political structure realistic? No, but it’s fun, so I’ll forgive it.
The thing that breaks people out of a story and makes them go What? is when the unrealistic thing is something they deal with commonly. If a SF character asks the replicator for a PB&J and it shimmers into existence, fine. If an urban fantasy character drops peanut butter, jelly, and bread into a blender and pulls out a sandwich, the story better explain how that’s a magic blender. Because that isn’t how it works, and we all know that. It’s why my wife the doctor can’t stand medical shows, while most people are fine with them. She can’t tune out all the stupid medical things they are saying and doing to appreciate the drama. Meanwhile, all that stuff is flying over my head and I’m way too busy wondering how Dr. Handsome’s drunken screw up of little Billy’s head transplant will effect his divorce.
Stories are unrealistic. The good guys don’t always win, true love only occasionally wins out, and there’s never a prophecy guiding everything along. Hell, there’s seldom an identifiable point. So I think not being realistic is not only okay in fiction, but necessary. Just don’t screw up the little stuff.