Tekashi 6ix9ine currently resides in a federal facility for government witnesses.

Although he's locked up, he's been able to hear the hate from folks like Meek Mill, Snoop Dogg, 21 Savage, Jim Jones, and Cardi B and he has a theory on why so many rappers have been so vocal.

6ix9ine's people tell TMZ that Tekashi believes that all those who have besmirched his name are jealous haters who are envious of his fast success.

6ix9ine intends on turning down witness protection when he released -- likely early next year -- so he can resume his music career.

He believes his snitching will soon be forgotten (T.I. and Irv Gotti agree) and he will make even more money than he did before.  Then he will wave it in the face of his haters.