Using someone as a vessel and possessing them are two totally different things.

[Though he's seen Laphicet overpower his human vessel and possess her, in a sense. Even then, one would have to be an insanely strong greater malak to attempt that.]

I can only curse people, and not intentionally.

[He says it like no big deal, but he really does think it's a big deal. Just... yeah he's tired of it all.]