The Atlantic has a long article out this month about Alcoholics Anonymous. The main conclusion: Alcoholics Anonymous is, for the most part, quack medicine with little scientific backing that is supported for historical/cultural reasons even though better treatments for addiction potentially exist.
It seems that everyone just assumes that 12 step programs work because of how widespread they are, but such programs (and apparently many other rehab programs) often have abysmal success rates. Furthermore, many of their methods are reportedly based on completely unsupported assertions rather than the kind of evidence that is usually required for most medical treatments. This is apparently a case where popular opinion has overruled any actual scientific evidence or consensus and the result is that many people are made to suffer unnecessarily. Treatment should generally rely on what has been shown to work and not what people believe should work due to some preexisting ideology.