I think people are misunderstanding what actually happened on that play. What's the upside for the Cards if Peterson tackles Lynch on that play? The Seahawks score a couple of plays later? What's the difference--you're down by three scores.
We saw this stuff two years ago when a defense has immense pressure put on it by a toothless offense--the defenders start pressing to force turnovers (Peterson here was going for a strip)--and the results are bigger plays for the offense that don't matter.
I agree it always blows my mind all the crap the defense takes after these losses. They gave up some big plays bit it didn't freaking matter, the second the other team scores more than 3 points against the cardinals; the game is over.
When the offense goes 3 and out EVERY SERIES, it's only a matter of time before the defense caves, it is flat out inevitable.