The two aircraft I have shares in are only covered for the syndicate members, and an instructor who is instructing them. Not an instructor without one of them. There's no mention of someone else touching controls.
I have difficulty visualising a situation where a sane and sober pax could cause an accident other than at take-off or landing.
I have difficulty visualising how, post accident, it could be determined that the pax caused it.
I can visualize a situation where a pax in a small aircraft could cause an accident, without any willingness by the pilot to let them touch anything.