First, he does seem right that most all of the mass murderers are male. There may be female mass murders, but mostly they are males.
Second, Americans are obsessed with death. Canada has a lot of guns, but they don’t have nearly the murder rate we have. Maybe it is a subset of americans, but as a whole, Americans do murder at a high rate for a civilized country.
Of course, most 3rd-world countries have a much worse murder rate, but I’m not thinking we want to compare ourselves that way.
We have a culture of violence and a lack of respect for life, and I think we need to fix that. Michael Moore is probably clueless as to how to fix the problem, but I think he is at least tangentially right — over the past 40 years, our culture has become more violent in this respect, even as many crime rates drop simply because of the fear of getting captured.
It has long been suspected that there are vast numbers of female mass murderers (serial murderers) who have been undetected....due to their VERY femaleness. Societal norms of judgement. Also, that these murderers are POISONERS, through food supply. There is an increasing amount of historical evidence for this.
Florida’s Black Widow Buenoano comes to mind— a real piece of work (executed electric chair).