Penn Station doesn’t have to be a homeless-plagued disaster zone — just look at Grand Central Terminal. Even before one vagrant’s stabbing rampage a week ago, local leaders shrugged off the issue, but New Yorkers (and New Jerseyans) have every right to ask why the city’s primary train station has to be a living room for mentally ill and homeless people . A few years ago, the lower-level food court at Grand Central was a mess, with vagrants camping out at tables and washing their socks in the