I think that if you have the freedom to choose your restrictions, then your chosen restraint can be really great for you, if you choose well. As someone that actually once upon a time had a far less than awesome marriage I know that's not a given, but I chose freely so I can own it and I do. I know plenty of people that didn't get to make these choices though, and some of them are stuck in bad places, and they don't get to experience much of that freedom.

Is it the act of prevention (and mind you this is targeted, so it's almost incomparable to generic restrictions to freedom) that makes it occasionally work, or is it that and reform, or even simply a lot of care and love and positive stimulation that does that?

I personally subscribe to the latter because I think that the act of taking something away on its own is likely to be perceived as a punishment and therefore often an invitation to regression, but maybe, if something else comes in the place of the addiction, there could be a positive result.