It affirms the unreality of the cinema aesthetic

Rating: 6/10 (16 August 2018)

I recommend reading my comments after seeing the movie, but if you never intend to see it, read them now:
The script gives its characters words we should not expect them to say, to express insights that should surprise us. The characters follow the path to cinematic fulfillment (the movie leads to a road trip). For all its appearance of social consciousness, Three Billboards is an entertainment.
The artful ways the movie delivers platitudes makes the platitudes seem fresh. The characters must be in darkness (since they're from Missouri?) before discovering that they can move into the light. They're supposedly racist and bigoted -- what does that have to do with finding or failing to find a rapist/murderer?
Now that I have asked, I offer an answer. The practice of racism and bigotry breaks down its practitioner's will to work overtime, and it reduces the incentive to explore the unknown.
Movie vengeance, however, is always worth the extra effort.

To demonstrate the degree to which one can work overtime, the fired police officer nearly kills himself to catch the monster criminal.
Ultimately, there could be a cover-up to protect the accused, who is a desert marine, in order to demonstrate the degree of bias the police can have in favor of veterans over civilians.
But the conjecture is for our own amusement. The piece is a construct, filled with incendiary randomness...cancer, suicide, torture, rape, murder, arson
(To quote memorable lines from Bob Dylan, "Abe said, where do you want killing done? God said, Out there on Highway 61" ... by the three billboards.).
These unexplained initial acts (How low can humans go?) are what make the movie possible.
As with Tarrantino movies (which get more entertaining the older they get) some human automaton out there must be willing to do a horrible act in order to test everyone's reactions.
In Mr. McDonagh's move (this one), the lines that resonate currently are spoken in the brick-a-brack shop "Did you do it?"
Answer: "No."
The unspoken further answer for the audience to add later is, "but I've been doing the same thing in Iraq."
Yes, I kept watching. Toward the half-way mark the surprises in cross narratives grabbed my attention and held me to the end. That in itself deserves my acknowledgment of efforts of all involved in creating this piece.
There is a Nicholas Roeg reference in this movie, which I see discussed elsewhere in the IMDB comments which I did not believe while watching.
In the movie, the movie on TV is "Don't Look Now," Mr. Roeg's Venetian Lost Child Thriller. "Don't Look Now" is scary. It doesn't mount social consciousness issues to create self-satisfying entertainment. (I'm thinking the resurgence of socially conscious entertainment began with the 2004 "Crash."
I like that this movie ends with the two major stars on a road trip.