I think people are over-reacting and don't remember that every season (including the Championship seasons) there were stretches when the team played soft, dumb, and just plain bad ... and most of those stretches Tim Duncan was on the court. Why I think people are freaking (and maybe rightfully so) is because this stretch is coming so late in the season.
This Spurs team is good. Up until this three-game losing streak they were on track to break the franchise win record. They have one of the best point-differentials in history. They have the best home record they've ever had. And a variety of other things.
Losing sucks and Spurs fans aren't used to it. But a three-game losing streak without Tim Duncan doesn't mean this whole team is crap. They need to adjust to playing without him. They haven't done that yet.
If 10 days from now they are still losing, then Spurs fans can cry, stomp, yell, scream and jump off the bandwagon. But right now, just let them come home and regroup and see what they are going to bring to the table.