Debunking doesn't work with most extremists, because they aren't following their cause for intellectual reasons.
They're following it for emotional reasons, becaues it makes them feel good inside, and they respond to the fantasies that are being dangled in front of their noses by charlatans.
Even if the truth is literally in front of them, they will deny it or say that their opponents are worse.
Debunking just makes them grip the fantasy more tightly.