I don't think its like Goldberg was at all.
I think with Cena you get what you get. Thats why turning him heel is pointless.
He is unique in the reaction he gets and until his fans don't cheer him or his detractors stop booing him, he'll stay where he is.
WWE would kill to have workers who split opinion like Cena.
Once he became this character it doesn't change, just like Austin, just like Rock, Bret etc. Principles are the same and that might be what you are referring to, but to say his character might represent some of his value, may be the truth, but thinking he cant separate WWE from real life is off.