What "rules about not lying"? Movies are entertainment. Most of them are based on lies, regardless of what it says at the beginning or in the credits. Actors are professional liars. Hollywood thrives in fiction; story and tropes.

Lies are distinguished from fiction by the intention to deceive about the real world, as opposed to counterfactual imagining.

Given that, what point were you making?

The point is, lying is bad, it rips the fabric of society. Fiction is not lying, it is useful, contextualized nontruth.

Lies are the lubrication of society; you're lied to anywhere between 9-200 times a day.

I see what you did there.

That depends on what the definition of "is" is.

That lying to people in order to make your film feel more realistic is a bad thing to do, even if minor in the grand scheme.

I don't think the intention was in any way to deceive the audience. I personally see it as part of their post-modern filmmaking[0] style.

What personally makes this style interesting to me is that there are usually several layers of meaning and intention. And usually references to other films or common perception or convention.

Even if the intention is to tell the truth or a true story, there's always the bias of the storyteller, the selection of what to tell, and what not to mention etc. So in this case, the Coen brothers re-used the "based on a true story" concept, and even exaggerated it. They re-use the format, but mock it at the same time.

[0] https://en.wikipedia.org/wiki/Postmodernist_film

It doesn't stop being an attempt to deceive just because it's self-aware, ironic, or motivated for other reasons. Likewise, murder during a robbery is still murder even if the primary is theft.

There are no such rules about not lying.

We have societal norms about it, maybe. But there are certainly no explicit rules about this, and the societal norms about lying are already pushed to their breaking point when you walk in to a movie theatre.

Rule and norm are synonymous, IMHO. What is the difference? What makes a rule explicit? Do you mean laws? Law itself is often rather abstract, does that still count as explicit?

I think there are specific laws about fraud. In film they can claim artistic license, though.