Filibuster Creep

Maybe someone can clear this up for me (any Congress scholars in the hizzee?), but why are we just assuming a GOP filibuster on the stimulus?  

I understand that, over the last two years, they've filibustered everything in sight.  But this seems like an odd inversion of how legislative debate has historically goes: opposition to a bill has never automatically implied a filibuster. Changing the expectation gives the GOP a huge advantage b/c they don't have to justify the extraordinary measure that is a filibuster with any arguments beyond those they would use to simply oppose a bill.  Shouldn't the burden be on them?  "Senator X, your party has lost two consecutive tidal wave elections, you lost the presidency and hold miniscule minorities in both houses of Congress, and the public holds you in open contempt.  Can you explain why you're trying to sabotage America's democracy in the midst of an economic crisis that your own policies have created?"  Has anyone ever bothered to pose the question this way?