Let's imagine that all the Bitcoin devs were arrested by a tyrannical government or bought by an evil mega-corp and forced to change a fundamental aspect of Bitcoin. Let us further imagine that this evil cabal managed to control 80% of mining power and used it to support the evil fork.

What aspect of Bitcoin, if it were changed, would make you reject such a fork and stay on the original chain against all odds? What change would you consider would destroy the fundamental virtues of Bitcoin?

Regular users, holders and nodes could block any fork by refusing to adopt, even against the devs and miners... but what is important enough that a significant majority would do so?