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You don't need payment processors to exchange Bitcoin, or rather, the processors are P2P'd and compensated by code enforced transaction fee. I guess those can be banned by manually correlating wallet addresses with known "terrorist" groups, but we haven't reached that stage yet.

The downside of not using commercial "off-chain" processors for Bitcoin or most true decentralized cryptocurrencies is that latency of a proper, classic, fully secure, "on-chain" transaction is something like up to 15 minutes. At least it was that much last time I looked at it.