Is belief in eternalism completely useless?

Is belief in karma due to eternalism completely useless? I do not know why those without self view believe in karma, but belief in karma is said to be useful, so does it matter if your metaphysics turns out to be mistaken? In which case, is eternalism a skilful means? More generally, I don't understand why lack of self view on paper, as an abstract belief you assent to, is very interesting or helpful. After-all, few people today believe in a soul, even a spirit.