Offhand, I believe that trick started with tribalism (generally, the 'other' is the most obvious scape goat), became racism in various forms (they look different / go to a different church it's /their/ fault), and has shifted to classism with thinly veiled racism included.

It's not much different than how a young child will blame anyone else for something that's gone wrong / they got caught doing. Maybe our society should do a better job promoting responsibility and allowing parents to offer oppertunities for children to be responsible; instead of infantalizing everyone entirely until some magical number has passed and suddenly they're an adult who was never previously empowered to be responsible.