I think you always want to be careful about getting too cute with these “apparent setbacks are actually good!” arguments, but I do think there’s a case to be made that Parker Griffith defecting to the GOP is, on balance, good for progressive politics. Organizations like the DCCC basically don’t care at all about ideology. And, indeed, in recent years it’s tended to make something of a fetish out of its ability to recruit and back quite conservative candidates to run in quite conservative districts. As a feat of pure political gamesmanship, it’s all very impressive. But having a Democrat win a seat and then assemble a conservative voting record doesn’t achieve anything for progressive politics.
Meanwhile, there are actually quite a few GOP held seats that Barack Obama won in 2008 and could conceivably support progressive members. In particular, Obama got at least 53 percent of the vote (his national average) in the seats currently occupied by Mike Castle, Peter Roskam, Mark Kirk, Judy Biggert, Donald Manzullo, Tom Latham, Joseph Cao, Fred Upton, Mike Rogers, Thaddeus McCotter, Frank LoBiondo, Pat Tiberi, Jim Gerlach, Charlie Dent, Frank Wolf, and Dave Reichert. Most of those districts probably couldn’t support a die-hard, down-the-line liberal (in particular, a bunch of those are rust belt seats that’ll probably never vote for an ardent environmentalist) but given that they all voted for Obama they’re clearly all places where a basically progressive candidate can win.
Which is to say that from the point of view of trying to maintain a progressive congressional majority in the 112th Congress, it’s probably more valuable to see money spent playing offense in those districts than to see money spent playing defense in very conservative districts. But the nature of the DCCC is that it doesn’t really care about ideology and does care about being nice to incumbents. So given a member with a very conservative voting record and a very conservative district, a defection that frees up resources for some other purpose is arguably a good outcome.
In an ideal world, some of these Republican members from progressive districts would cross party lines and cast some votes in favor of progressive policies. There has, however, been weirdly little of that in the 111th Congress.