Earlier this month, private-equity firm Fortress took its mortgage servicer unit, Nationstar Mortgage Holdings Inc., public, the second such offering for a mortgage servicer in a month, even as some large bank servicers increasingly look for the exits. The move might look like healthy creative vs. destructive capitalism to some, but it’s a disturbing trend on at least one public policy level, according to housing policy expert Karen Shaw Petrou, managing partner at Federal Financial Analytics, a Washington, DC, think tank. “From a purely market perspective, there’s no problem if banks lose and PEs win ...