Linguistics; history of language
Polari is a linguistic deviation. So is Ebonics -- whether the original term referring to the language of all descendants of Black African slaves, or the modern term of Vernacular English. It's language, it evolves and changes and combines into something new & interesting.
There are people that would frown on that idea. There's also people in Singapore who look down on Singlish. Or Spanglish. But that's a linguistic deviation. It's valid. It's legit.
Linguistics; history of language
And in languages, lingual drift is what you get with population drift. That's a big reason why there were so many different languages that made it hard for people to communicate. They split up.
You get populations splitting apart, coming back to meet each other, and then coming up with whole new words that were really your old words but different now. (Example: "shirt" and "skirt" used to just mean "skirt", which is to say shirt. English dropped the k to h)