This seems like a film that is impossible to talk about in any real fashion without spoilers.
In comparing two films from the past year that both look into certain aspects of rape culture, this is a bull in a china shop approach next to The Assistant's banality of evil approach. I found The Assistant astute and insightful and thought it deserved so many Oscar nominations instead of none. Promising Young Woman got numerous nominations but leaves me pondering whether this film is actively harmful. There is a cinematic dynamism to the storytelling--from a moral standpoint it seems in line with I Care A Lot--but there's kind of a nasty nihilism about it that suggests such a rigged game (and such an awful humanity) that the only solution is self-destruction and immoral retribution.
"Not all men" is kind of a joke at this point as a means of deflecting critique against general patriarchy/mankind in society. This film's world pretty much says "Yes All Men" but importantly, that is from her perspective, and her perspective suffers from selection bias. Using her tactic of acting pass-out drunk in clubs to draw "nice guys" that take her home but inevitably try to take advantage of her, only to reveal herself to be fully sober, she kind of does a scared straight routine. Each man is added to her book of shitty men. Not added to the book are the men who don't try to take advantage of her because they aren't at the club in the first place (and I think night clubs probably have a disproportionate number of awful men). I take none of this lightly as I have a friend who was assaulted by a guy who took her home drunk, a guy who was a very close friend of hers, not some random stranger, which is probably the more real threat. But this is a testament to the film's worldview.
In the middle section we get two parallel tracks, Cassie trying to open herself to a relationship with Ryan, who seems actually decent, while at the same moment putting into action a scheme of retribution against those she sees as complicit in the assault of her best friend years back (the cause of her dropping out of medical school and generally stalling in life). Her methods involve head fakes where on the surface they seem vile but we find out they are perhaps just murky. As someone on the record of not buying into two wrongs make a right logic, or of working outside due process, this definitely poses a challenge in your perception of her.
The film ends with her getting a measure of justice, through the creation of some new injustices, and at a personal cost to herself that certainly doesn't make it feel anything like justice. On the one hand you have the undoing of Ryan, revealed to have been a witness (though I didn't get the sense he was a participant) in her friend Nina's assault. The Assistant does a good job of depicting how someone might know the truth and feel unable to act, to be unable to call out something bad in the moment...and critiquing it has a bit of the nature of those who doubt victims because "they should have reported it." More overt is with Al who, as much as we might want to see him held accountable, could reasonably claim he acted in self-defense in killing Cassie, though in a turnabout from the initiating incident, no one would likely believe him (especially after he and his Best Man display a guilty conscience by getting rid of evidence). So yeah, I don't think this film does anything to further understanding or to make improvements, it just looks around and decides that everything sucks so you might as well take part in burning it down.
It isn't a coincidence that the moments that stand out most in the film, her conversation with the defense attorney who got Al off (played by Alfred Molina) and her conversation with Nina's mother (Molly Shannon), are the ones that embrace humanity and redemption the most. I don't know, maybe anything happier would be lies (The Assistant certainly doesn't give us a happy ending either), but if you give up on hope you have nothing. It makes me think of the end of Get Out as compares with the original ending. Or the finding that while a lot of success and failure has limited connection to personal effort, believing that personal effort is vital does tend to boost success. Sometimes lying to ourselves to create hope or motivation is essential.