In AP Psychology class that I took in highschool, I had a chance to read about the concept of 'Defense Mechanisms' proposed by Sigmund Freud. His list was quite long, somewhere around 10, including projection, aversion, and etc. However, except one or two, the essence of those mechanisms were identical: human beings tend to look out for a reason to blame to contain their anger.
Mildered is not an exception. From the very first part of the movie where she visits the Ebbing Advertising Company, we can easily notice the anger of a woman who decided to dedicate her life to take a revenge on her daughter's murderer-raper. Renting three billboards which has not been in use for almost 30 years due to limited volume of traffic for $5000 a month, her overconsumption demonstrates the fact that her anger has already taken control over her reasons.
However, the target of her anger - the cause and causality of her anger - remains highly obscure. In 《Prologomena to Any Future Metaphysics》, Kant said that the law of causality is pre-exprential concept. That is, the law of causality is not based on absolute logic. In fact, even the scientific causality might be a mere accumulation of simultaneity with statistical significance in a way. Thus it leads us to a conclusion that causality of human matters are even more elusive. For instance, what should be a real culprit for your failure on exams? Friends who asked you to hang out? Your laziness? Professor's personal opinions?
Mildred's choice of messenger, an advertisement, symbolizes such indefiniteness. Although those billboards are aiming at chief Willoughby, the characteristic of 'billboard advertisement' aims everyone in the town. It is exemplified through her unreserved aggressions towards her Father, dentist, ex-husband, and even her own son. Her interview saying 'The buck's gotta stop somewhere', or her rampage towards the Father regarding the new gangster law suggests that the target she chose for her anger is undoubtedly not based on throrough rational investigation.
Consequently, such haphazard expulsion of anger alienated her from the rest of town community. It is obvious that no one wants to come across sudden calamity engendering from her anger. And once the anger points at a wrong person, the alienation easily transforms into hatred. After she had harassed chief Willoughby - a revered man in community, a man of thorough conviction, a man who appears to be unfriendly but never losing faith in justice, and a man who is about to die - that is what exactly happens. Sharp contrast between her rashness and Willoughby's understanding, which includes absolving Mildered and eve payingfm for the billboards, makes Mildred appear even more imprudent to others.
It is true that anger does not necesserily end up negatively. As if firefighters sometimes set fire to counter bigger fire, Mildred's straying anger inhibits that of Dixon. He who discriminates colored people, pummels down the poor advertising man, and inflammates billboards finally 'ebbs down' his anger due to the flame bottle that Mildred threw at him. As a result he has a half-burned mask, which reminds us of Harvey Dent from the 《Dark Knight》. The only difference is while Harvey turned from good to evil after the burn, Dixon shows a clear opposite change.
Nonetheless, those few positive effects cannot justify carelessly roaming anger. Even Mildred herself is well aware of this fact. Although determined and robust on externally, she easily breakes down after recalling the last conversation she had with her daughter or becoming aware of her daughter's last request to her ex-husband. Just as Willoughby had advised Dixon through the letter or her ex-husband's girlfriend as mentioned, she might have had to look through the essence of anger and start over with reflecting herself first.
Unfortunately, this is not the case. She evades from self reflection just as she didn't face up the truth from her ex-husband. Instead, her anger transfers from Willoughby to a plausible suspect discovered by Dixon. A concrete alibi does not hinder her or Dixon from taking personal revenge. Both the Mildred and Dixon are 'not really sure' about killing the suspect, but they decide figure it out 'along the way'. Such inconsiderate attitude shows us how lost their anger is.
An American guy whom I met recently told me that this movie is seminal these days in America, corresponding to the 'Black Lives Matter' movement. However I think what this movie tries to say is quite opposite. Although it might appear as criticizing discrimination against colored people, it in fact tells us that such anger is destined to be lost. Modern society is known to be a place where it is hard to point out who the culprit is. Furthermore, even the law of causality seems to be unstable. If so, is it even possible for us to direct our anger towards where it should be aiming?