If they actually have autonomy, then you can't truly "cause" them to make a particular choice.

Are you seriously assuming incompatibilist free will? If we've got (roughly speaking) a deterministic universe, and no Kantian nonsense about noumena, then everybody can be caused to do things, even though they're autonomous.

Unless you're assuming incompatibilism in absence of free will... in which case, it seems like you should have a more basic disagreement with the objection of not treating people as though they are autonomous.