Its technicaly true that its impossible to force someone to do something that they would absolutely refuse to do under any circumstance. However people are willing to do a lot of things that they don't realize that they're willing to and its possible for people to change what will and won't do in response to their environment. Hypnosis can amplify both of these effects. Given enough skillful hypnotic manipulation over a long peroid of time, it is possible to eventually convince someone that any given course of action was something that they wanted to do all along.