Writer's point of view: What have gone wrong and how it could have been fixed?

Rating: 8/10 (27 October 2019)

I will try my best not to make this review long, I will sum my opinion in two points.
I watched Joker with two mindsets, I am a Fan and I am a WRITER. The fan inside me is pleased but the writer asked for something, and would not settle with "it was OK"
1- The quick escalation of events:
I understood the movie and its message very well. I congratulate the writers of this movie for making such a unique take on the joker, and I liked the sequence of the events until the final act of the film. There is a "missing chain of events"
As a writer you need to ask yourself the following questions:

Why all the people in the sub-way were wearing clowns masks all of a sudden?
Why there were riots against policemen? Is it something logical you would do as a law abiding citizen that you hear about a crime on TV, and then instead of sympathizing with the victim you would hold demonstrations along with other persons you do not know and wear the exact same mask and take the same sub-way train and head towards the same destination !!!!!!!!!. Who would even sell that mask and where can someone get it at that time (70s)?

What you need is a driving action/ a motive / a call for action/ a missing sparkle. Right ?
Here's a suggestion:
What if after Arthur had killed the three rich-boys, two policemen assaulted a random guy who dresses as a clown, (like if it is his night job or something), and we were seen scenes where it is prohibited to wear a clown mask or dress like a clown and we were shown a number of arrests in the background of a random scene where Arthur walks by and a policeman arrested a clown.
and all of a sudden the above mentioned random innocent guy who were assaulted by the police died as a result of that assault and the word has spread across all media news papers and TV and it turns out that the guy has nothing to do with the murder of the three rich-boys and as a sequence of that event People demonstrated wearing clowns, and there are clashes here and there between the security forces and the angry mob until Arthur appearance on TV as Murray thought that would be a Hit, to show a person (who works as clown) who he personally mocked and now reconciles with him and then BANG until the End of the movie and you know the rest.
2- The not-good overly used good elements:
The Dance was overly used. I believe if you are going to use Dancing as measurement of how a person is in control or to symbolize the state of mind of a person and how he has become the Joker of the film and it is a dance of glory and confidence, then it should have a purpose, they could have used it as if his job depends on him to perform dancing routines for children but he could not because he cannot dance, and he struggles throughout his career as a clown to be getting paid less or being ignored by his employer for that reason and now we get to understand why his fellow clowns take more advantages than him and why his boss wanted to fire him and of course not because of a stupid sign, imagine if you get mobbed and beaten in the street and then someone blames you for losing a stupid sign. This is not logical.