There can be consensual but harmful activities.

Almost any consensual activity can be harmful if taken to excess or without caution, such as smoking, driving, swimming in the deep end of a pool, etc. Caution and education deal with these problems much more democratically than prohibition. It's the matter of consent that makes it important.

And there can be nonconsensual activities which are harmless or beneficial.

It would be interesting to see you make a list of such activities that are non-consensual but benign, let alone beneficial. And it all depends upon whether or not it's a life or death matter, otherwise it's best left up to the participant to decide whether or not a certain action has enough potential benefits to be worth taking. For instance, forcing someone to get psychiatric treatment if they are a danger to others can indeed be seen as beneficial, except it's well known that people can often only be helped in such instances if they want to be helped, and if their ego allows them to admit they have a problem.