With small blocks when "outlaw" transactions become difficult to get mined due to blacklists, the senders of those transactions simply need to up the fees to the point where it is profitable to setup an anonymous mining operation behind Tor or some other anti-censorship technology and start mining those transactions. Provided >50% of the hashing power is willing to build on those blocks the transactions will get into the blockchain.

With large blocks, setting up that anonymous mining operation at best requires access to large quantities of anonymous bandwidth - not a trivial thing to obtain - and at worst is impossible because getting a copy of the UTXO set can be made impossible without revealing your identity.