It's also undeniable that until the Victorian period, Europe was generally becoming more orderly. (You'd probably see a drop in testosterone levels if you could measure this.) The trouble is that we live on the other side of that curve. See under: http://en.wikipedia.org/wiki/Sensitive_urban_zone. ("ZUS" is French for "no-go zone.") But fudge and blur enough and you can hide the peak.
I'd love to see Professor Spierenburg take a walk in Les Musiciens someday. His name sounds Jewish. Perhaps he'd be kidnapped, tortured and burned alive, like Ilan Halimi. But before he died, would he change his mind? Statistics suggest the contrary.
And what about Union busting. 50 people died from http://en.wikipedia.org/wiki/Paint_Creek-Cabin_Creek_strike_... can you imagine what would happen today if the same level of violence became national news? Yet, for the time while it was larger average such things where not all that uncommon.
Looking at http://www.deathpenaltyinfo.org/murder-rates-nationally-and-... you can see a 11x difference in 2010 murders between Louisiana 11.2 and New Hampshire 1.0. But, considering the amount of migration within the country I think a national perspective is necessarily. And nationally, 200 years ago things where a lot more violent.
PS: Granted, it's not hard to twist these statistics if you include vehicle accidents the numbers start to change dramatically.
http://www.newyorker.com/arts/critics/atlarge/2009/11/09/091...
Philadelphia is one of many city's in the US, but looking at the overall trend and including things like duels shows a different picture. Consider, some gang violence would not have counted as murder 100 years ago.