The reality is, just a few backup witnesses have very little influence and by themselves can do next to nothing to protect the chain from core changes which might include censorship as we're already seeing on the Steemit interface (along with attempts to justify it) along with massive downvotes from the stake that was supposed to be used to benefit the Steem community.

How many witness positions would an attacker need to control in order to censor certain transactions... like exchange deposits that look like Hivians exiting Steem?