A friend on here just sent me this by one of the authors of the book. In The Freedom Model, happiness is the central motivator of change, but you don't need to be happy to solve your substance use problem. - The Clean Slate Addiction Site
What I took away from it is that they are trying to help people get to the place where they are ready to decide what to do about their substance use. They don't believe in treating underlying causes, they think that's bunk. I agree with all that. I think the only reason for talk therapy should be about helping a person come to a decision, I think "underlying issues" are AV. My AV always had an answer to everything, "Let's have a drink!" In fact, my AV created problems for me to drink over lol.
They also aren't saying that quitting is the road that leads to happiness. They are using happiness as a motivator to true internal change. Getting people to question if substance use is actually delivering the happiness they are seeking or if there is a better way. It's all about perceptions and beliefs, the stories we tell ourselves.