That's "consensus" from the perspective of language -- full agreement from each any every participant. That's what "consensus rules" are: those rules that each any every user consents to by virtue of opting into the network (running a node).
But that's basically impossible from a technical standpoint. Just by virtue of laziness/inertia/ignorance, there will always be those who don't upgrade. And beyond fixing blatant protocol flaws, you will always have those who oppose. That's why I'm of the opinion that Bitcoin technically can't ever be hard forked and still remain "Bitcoin." We would be moving to an altcoin if the fork were successful. And maybe that's okay... but I think we should be clear about what hard forks are. A hard fork = leaving the consensus to join a different one.