To me, the phrase implies murderers and murders are common, which isn't true.
Do you have any idea how many people were murdered last year? How about last century? Murder is very, very, very common.
Out of every one hundred people you meet, five are psychopaths who would love nothing better than to commit murder. Only fear of getting caught stops them. Sometimes. About half a million people are murdered worldwide each year.
This is only part of the story. Another one and a half million are murdered, but the person committing the crime has it plea bargained down to a lesser charge, so it doesn't count on the stats. Another five million attempt murder, but are stopped. Another million go missing, and will never be heard from again. No one knows how many of these are murder cases, but of these missing, only the dead are ever found.
This doesn't even count most of those murdered in wars. I don't mean soldiers killing soldiers, I mean actual murders than are simply listed as casualties, if they're mentioned at all.
Maybe murder is uncommon on a percentage basis, but all those numbers of two or three per 100,000 are grossly misleading, and by design, barely touch the actual number of murders.
This also does not count such mass murderers as Pol Pot, with ten million murdered. Never mind Hitler and Stalin. Between the three of them, they murdered nearly thirty million people.
But I'm just talking about civilians killing civilians.
Murder is certainly far too common for my taste. People love killing other people. If they can't do so by outright murder, which millions have done, they'll start a war. WWII alone killed at least fifty-five million people.