Your statement is shit. "Some guy I knew a long time ago once used threads for some unspecified purpose and when he got to thousands of threads it become very slow". Well that is just great. What was he trying to do? How was he trying to do it? You act like your anecdote proves something but without this information it contributes nothing to what could have been an interesting discussion.
Since the discussion was originally about COBOL, are you suggesting that language is more suited to massive multithreading than Java? If so, why? And if you truly need thousands of threads, perhaps you need Erlang?