Such a spread of potential situations, it is hard to generalise.
- Hypothetical: Is going a little deeper, or in water a little murkier, or colder, than someone is really used to going a "trust me" dive? Not such a biggie.
- Hypothetical: Putting unqualified divers on Nitrox where there is a hard floor of 50 feet is a "trust me" dive, and I have seen people freak on SB at that very suggestion, but how much risk is there really?
- Real: I was once asked to lead two less experienced divers on a dive in a cavern I had never been in before (neither they nor I were cavern trained). We had all trusted the instructor who set up the groups; coming back I was pretty upset about it; I felt I had been really misled as to how potentially risky the dive was - the others who went with me just couldn't really see what all the fuss was about.
- Real: A friend of mine, who is not cave qualified, has been taken cave diving by her boyfriend and his cave diving instructors in DR. That strikes me as pretty unambiguously over the line.