In fact, whether it was learning about the ten commandments at school back in the dim and distant past, I think it would be fair to say it was always part of a collective consciousness that murder was just about the worst thing a person could do, and maybe that was reinforced but heftier sentences, and capital punishment here up till about 1963 I think.
We've always had gang warfare, The Krays for example, that encompassed psychopaths, but there just seems to be an awful casualness about the taking of life amongst the very young knife carriers of today, as if it is some rite of passage and badge of honour to take out some poor innocent kid.. The enormity of taking a life seems to have been lost on the perpetrator.