Ricardian equivalence states that a deficit-financed increase in government spending will not lead to an increase in aggregate demand. If consumers are 'Ricardian' they will save more now to compensate for the higher taxes they expect to face in the future, as the government has to pay back its debts. The increased government spending is exactly offset by decreased consumption on the part of the public, so aggregate demand does not change.
This is not just wrong, it is flagrantly wrong. I'm sure everyone has their favorite examples of Wikipedia falsehoods, so I'm not saying anything new here. File under: The Wisdom of Crowds: NOT!