When it comes to fantasy, I don’t mind if a writer ignores reality. This shouldn’t be that odd. Fantasy is, by definition, an escape from reality. Or, if not an escape, at least a chance to see a world that might have been. The important element is that, either way, fantasy is just reality as we know it with a tweak here or there that allows the impossible to happen.
I go into fantasy with eyes wide open, knowing that reality can be, will be, discarded if it allows a human to teleport or an invasion of space robots. I don’t need a justification beyond this is fantasy, and that’s what makes it awesome.
I know writers who work hard to justify fantasy. Just the other day, someone told me that if they were going to write a story with someone who turned invisible, they’d have to come up with a reason why that person wasn’t blind at the same time. It’s a legitimate question, or it would be if becoming invisible was something that could actually happen in real life. But it can’t, and unless the goal of your invisible man story is to make someone think being invisible would stink, then it’s counter productive.
This is the “Superman would kill Lois” fallacy. It comes from a well-meaning place, but it misses the point. Superman (and much of fantasy) isn’t meant to be realistic. Superman, like most superheroes, is not intended to be a horror story about a superhuman who accidentally crushes to death everyone he loves. It’s a mistake to approach it from that angle, even if to do so is with the best of intentions.
This is why I prefer fantasy to science fiction. Even my science fiction stories are fantasies. I can’t give you a reasonable excuse for death rays, robots, and alien life forms. I just know that they’re neat, and that’s really all I need to know.
Fantasy elements should have limits, but those limits don’t need to come from reality itself which already has the biggest limit of all.
I’m sure if I tried very, very hard, I could come up with a semi-believable reason for why getting bitten by a radioactive spider would give someone superpowers. I know there are writers who strain to justify integalactic travel against the unforgiving limit of the speed of light. And if anyone thinks there will ever be an even remotely scientifically plausible justification for telepathy, Hulking out, or dragons breathing fire, they’re more optimistic than I.