That's not strictly true. For instance if you were under and told to kill your mother or someone you knew, cared about then the anxiety that produces would be sufficient to bring you out of hypnosis. However if that reality was changed so that the person you cared about was not perceived to be that person (doesn't have to be someone you care about either, just someone/thing where your internal morality could kick in to prevent you)....

I think in the 40's or 50's the US experimented on US soldiers, and one officer was told that the next man to come in the the room (something like that) was a Japanese soldier about to kill him (might have been German but you get the picture, he was told it was an enemy about to kill him) when someone entered the room he legit tried to kill them before he was killed (as he believed). The guy who entered the room was his Superior Officer, but he didn't see that he saw an enemy soldier. So effectively if you change the reality of the subject so it becomes morally acceptable to do harm, then that apparently is successful.

Scary ain't it. Our minds are very malleable.