How far is too far? If I was the confidant …

It is interesting thought. I think it all depends on the personal limits, and while it sounds fun and edgy “Do not interfere!” and I would not, as long as I did not perceive actions as life threatening or permanently damaging! But than, permanent damage does not have to be necessarily physical, and while I would not stop gang rape or bestiality - would my friend be damaged for life by the experience of that sort?