We are so used to celebrating homeownership in the United States that it's a little starting to hear it criticized. After all, home owners bring stability to neighborhoods, in part because they have a financial stake in how they turn out. But some researchers think that, on balance, homeownership is a bad deal for cities. For one thing, they say, it tends to increase unemployment by cementing people into places they really ought to leave. More surprisingly, some research indicates that high levels of homeownership might deter entrepreneurship.