The New Republic has sorted it all out for us. When Republicans use the filibuster to restrain a Democrat majority, it’s unconstitutional, and just plain evil. But when Republicans are the senate majority, the filibuster is a very important tool and should be used “ruthlessly” to make sure Republicans can’t accomplish anything.
New Republic, November 21, 2013: Stupid filibuster!
New Republic, November 4, 2014 (just after GOP retakes the Senate): Second look at the filibuster?