Doherty locked up for drug use and death of friend. Whats the point?

Pete Doherty has been locked up after footage taken by a friend who died of taking drugs was found of him also using crack. Does it makes sense to lock up an addict? As far as I can tell he hurts no one but himself and prison does not seem to cure him. He surely can't be held responsible for the death of his friend, an adult, who presumable was free to decide for herself whether or not to take the drug that killed her...

If the reason for locking someone up was to try to break their habit then that will clearly fail as anyone who watched the recent documentary series following female prisoners in Scotland will know. They seemed to have almost free access to heroin on the inside as they do on the outside. In the mean time the nations tax payers pay to fill our prisons at considerable cost and rapists and murders get released early so that we can accommodate then. Shameful