Why Can't People Be Forced to Stay in Rehab?

I watch this show called Intervention on A&E and it's moving, interesting, and sometimes very sad. The people on the show think they are participating in a documentary about addiction but what they don't know is that an intervention is being planned. You get to see them doing drugs, how their lives really are, how the families are affected, and you get to see the pre-intervention meetings. Sometimes they go willingly, sometimes they go just to please their family. Sometimes they stay, and other times they get kicked out right away. 

This brings me to a question I often find myself asking, why can't people be forced to stay in rehab? I know sometimes people get told rehab or jail because they've committed a crime or continue to get busted for drugs or things associated with addiction. There was one woman on the show who was addicted to shopping and she got credit cards in her mom's name and that's a major offense. But back to my question. I'm not making a moral judgement and I'm not talking law here, but if the person is a threat to society (just as a drunk driver would be) and are truly addicted and have a disease, why are they able to walk out after an hour, a day, whatever? 

I can think of what people might say, something like they can't be forced to want to heal or to change. That might be true, but it seems like it's might dangerous to let someone drive around high or drunk all the time. Maybe if they knew they couldn't get out willingly they would commit themselves fully. How many times have you looked at someone like Amy Winehouse and just wanted to strap her down for a week and not let her go anywhere, or even Britney, even though hers is more mental? I have totally said to myself that I would take the "I'm locking the door and you're not going anywhere" approach. You know, they might hate me for a week but at least they'll be detoxing. 

I'm just thinkin'  aloud here, maybe you guys could give me your thoughts?

In the meantime, check out this site where they have before and after pics. Yikes!