people panic -- if you've got a gun and are having an emotional response of some kind, anger, fear, what-have-you, someone could easily get shot when otherwise they wouldn't
Ref:
https://americangunfacts.com/pdf/www-telegraph-co-uk.pdf
"2034[1] vs 466 Violent Crimes UK vs US per 100k people"
[1] The July 2009 Telegraph article says "over 2000"