Theft for the greater good?
Why do you keep insisting on calling this theft? Nothing is being stolen. The miners would simply be refusing to aid what they believe to be a theft or fraud.
I agree, it is a change of the protocol, however, none is stealing the private keys of anyone else.
Miners discarding the valid blocks of miners who refuse to engage in the unethical blocking of wealth based on no due process is extortion and tantamount to theft of the block reward.