You go to work with the language you have, not the language you want.
The Fowler brothers thought that English would be tidier if we used that to introduce restrictive clauses and which to introduce nonrestrictive clauses. Prescriptivists have seized on that suggestion and persuaded many editors and some writers that it is a Rule rather than a recommendation or pious hope.
And at Lingua franca, the erudite Anne Curzan looks at people's disdainful objections to the slang word legitly. Legit, its immediate ancestor, retains the smell of slang despite its long use as an adjective. But legitly, she points out, is a regularly formed adverb; it follows the morphological rules. And, moreover, "slang is a completely legit—and informal and sometimes rebellious—form of language."
This is how English works. Slang bubbles up, and some of it stays.
You don't have to like legitly; you don't have to use it yourself; you can probably keep it out of formal writing for a long time; and you can moan quietly to yourself in the chimney corner if it hangs around long enough to get included in dictionaries.
Just stop carrying on as if the normal processes of language were some kind of personal affront.