Could The Untouchables be interpreted as a pro-right-wing/conservative movie?
It was afterall made at the height the Reagan era. And maybe one way to look at the heroes' methods if that they have to employ a "shoot first, ask questions later" mentality. This is emblematic of Malone's "If they have a knife, you bring a gun" speech on how to deal (AKA "The Chicago Way") with Al Capone. Or the part where Ness is pretty much forced to take matters into his own hands (so to speak) instead of taking the chance of Frank Nitti being prosecuted (and likely let off, as he had arrogantly boasted).
https://www.theguardian.com/commentisfree/2016/dec/26/liberals-far-right
https://www.theawl.com/2011/06/was-david-mamet-ever-really-a-liberal-anyway/
https://www.csmonitor.com/1987/0604/ltch.html
http://conservativemovies.blogspot.com/2008/11/untouchables-paramount-1987.html
http://filmhistoryus.umwblogs.org/the-untouchables-the-film/as-a-primary-source/