Okay...
So did you not see the outlier in society? The bullied, the cast aside, the ignored, the disenfranchised...?
Yes, the film is shrouded with darkness, but throughout all of it, the opportunity of kindness is there, offered or not and we ALL make those choices.
The 'murder' and subsequent 'dance' stuff is a relief valve/ a victory against his tormentors and whilst I agree it's not 'nice', you would have to understand these things were avoidable if people gave a shit more.
I found myself wondering who was really wearing the mask in 'Gotham' which could be extrapolated to general society if you cared to go down that road.
Maybe watch it again with a different mindset and see if you reach the same conclusion?
The film is, indeed, worthy of discussion.