The many complaints about San Francisco's declining quality of life notwithstanding, city officials have been taking bold measures to ensure that you'll never have a problem finding a conveniently located crack dealer when you're jonesing for a hit.
Despite the city's best efforts to protect its large population of undocumented street entrepreneurs (in non-SF-speak, illegal immigrant drug dealers), from time to time a few of these enterprising individuals do get caught up in a police sweep (most likely one conducted by the Parking Division, which seems to be the only arm of law enforcement actively seeking out criminal conduct) and are subsequently convicted of selling drugs.
Which in turn not only makes them liable for substantial prison sentences, but also requires that they be deported to their home countries and permanently banned from returning to the USA. Worried that San Francisco's homegrown criminal culture might be unable to generate sufficient numbers of crack dealers to meet demand, the city has spent a small fortune and broken a few laws of its own (hey, it's only money, and everyone knows that normal laws don't apply in SF) to hide its convicted crack dealers from the federal officials who handle deportations.
It's "not fair to bar them from ever becoming citizens," said one San Francisco official, who rather judiciously preferred to remain unnamed. The sheriff of San Bernardino County, where San Francisco had been hiding its fugitive felons in a taxpayer-financed ($7,000 a month per perp) safehouse, was not so sanguine, especially in light of the fact that SF's city-sponsored crims usually end up taking a hike and slanging rocks on his patch.