It’s a lockup with an open-door policy. A new detention center in San Francisco designed to hold recently arrested drug users allows detainees to simply walk out if they please. The downtown center, which has been pitched as an alternative to jails or hospitals, provides officers a place to take publicly intoxicated people to sober up and access addiction treatment.  The downtown center, which has been pitched as an alternative to jails or hospitals, provides officers a place to take publicly intoxicated people to sober up and access addiction treatment.  Anadolu via Getty Images The facility is meant to keep users off the streets while allowing police to return to their patrols, relieving them of lengthy paperwork required at jail intake.  But once inside, detainees are free to leave. “Technically, they can walk out,” Rani Singh, chief legal counsel for the San Francisco Sheriff’s Office, told the San Francisco Standard .…