I've seen this argument over and over again, and it's ridiculous. Saying "humans are not rational" is not the same as "humans are never rational"
The statement is made about perfect rationality. No, humans are not perfectly rational, but it does not follow that humans are never rational or unable to be rational.
Is it a good idea to assume non-rationality in policy, though?
As I also wrote in my other post, I think one can easily argue that 'more informed policy' that 'accounts for human's partial rationality' actually creates complexity which makes it even harder for humans to act rational.
The statement is made about perfect rationality. No, humans are not perfectly rational, but it does not follow that humans are never rational or unable to be rational.