If you're still here:

Definition of rationality- The ability to determine truths based on what is justified by the evidence avaliable. Generally requires a degree of ability to compensate for cognitive biases. Definition of 'pure rationality'- Perfect ability to make justified interferences based on the evidence avaliable. Implies complete immunity to cognitive biases.

These are both tenative, but close enough to show the flaws in your argument. Pure rationality as defined may be practically (if not theoretically) impossible, but is a reasonable goal.