Your response would be accurate if you had not added "at least in potentia" to your critique of human rationality.

As it stands, Douglas is correct: you are making a rational argument that humans cannot be rational.

To that, I non-rationally say:

This game that you play does not look fun. You pretend a thing, then don't, to make sure you are the one who wins the talking game. I don't like that game. Don't wanna play. I'm gonna play someone else's game where they make me feel like when they say something, they mean it, so we have a nice game where we both have a chance, not a you-always-win game.

I now rationally say:

Of course we humans frequently employ rationality as one of a variety of cognitive strategies. What wasn't sufficiently appreciated by Enlightenment thinkers was that it's the intuitive dog wagging the rational tail a lot of the time, and one can make that point quite well (e.g. Jonathan Haidt does in Righteous Minds, albeit with an elephant and rider rather than dog and tail) without making a self-refuting argument by simply not overstating the point.

Our culture has not stressed a careful, rational, evidence-based approach to important matters, so although your clients provide an abundance of data about how people in this culture tend to be now, it can't answer the question about what our potential is to start applying more rationality even in the most emotionally fraught circumstances.

One might suspect, in fact, that overstated claims of impossibility of rationality would further accelerate our divorce from it, leaving us fundamentally adrift in a complex world. One might at least want to ask: have we been abdicating our duty as a society to teach people how to embrace this way of thinking, given how incredibly important it is when our species has immense power and has manufactured an environment of immense complexity for which rationality is an essential tool for comprehension?