The inhabitants of London are called Cockneys.
Cocken Ee = a cockerels egg, hence, something utterly useless.
I do suspect that labelling of groups and individuals happened as soon as language developed to do it with.
It's a way to avoid thinking.
So if you suggest that there are too many immigrants.
I call you a fascist, and that means I don't have to think about the actual numbers, origins, costs and benefits of immigration.
By labelling you, I've demoted you to a category of people whom I can ignore, or, if it comes to it, fight a war against.
No need for thinking at all.
Cheers
Dave