PPOI was built in 2023 to solve a problem no one else had figured out; base-layer privacy without attracting malicious activity. It scans transaction history before allowing access to shielded pools. If your address has interacted with flagged protocols or sanctioned entities, you can't shield. Clean history means privacy works normally, compromised history means it doesn't. RAILGUN has no admin keys, doesn't custody funds, and can't freeze your assets. The protocol is fully permissionless, but PPOI acts as a filter based on provable on-chain behavior.