From what I gathered by reading the whitepaper mass censorship is extremely hard to accomplish.

>Could ISPs throttle or block IPFS content, for instance?

They wouldn't know what was IPFS and what was regular encrypted TCP, the only way I can tell IPFS traffic apart in wireshark is the port number. Once ISPs start blockings random encrypted connections people will get mad when their games or other applications stop working.

If we are talking about bad actors in the IPFS network, I reccommend you read their whitepaper. They layout a clever karma based system for incentivizing nodes to help others and punishing nodes that misbehave.