You're right - re-reading, I meant to say "people behaving irrationally have collectively unpredictable behavior", to which I assumed you would agree. I was extrapolating that from here:

Irrational thought patterns can be nearly anything, so there's no way to specify an argument that will convince everyone.

I had also argued in the past that one could construct arguments that would convince most people since they're probably irrational in predictable ways, and you disagreed.