OK I won't get into an argument of whether stereotypes or prejudices are good/bad and I'm sorry if I implied that. I can't speak for the GP (u/alexk), but I interpreted his assertion of
"People should try harder to decouple their biases from facts especially in their public writing" as saying that using stereotypes as factual evidence leads to weak writing.
For example, this graf:
> Yet if these people or their friends were the only ones who had contact with your data, no issues at all. Slovaks, particularly in the service industry, are astonishingly honesty.
> [the next section is about how technical work is outsourced from Slovakia]
The author apparently thinks IBM's off-shoring would be fine (indeed, "no issues at all") if the work outsourced to Slovakia stayed in Slovakia (rather than be outsourced to India), and his supporting argument is that "Slovaks are astonishingly honest". Take away the stereotype, and we see how flimsy the author's assertion is. It's not the stereotype that's wrong, necessarily, it's how the author uses it as evidence.
Yes, I suppose I agree with you that people being explicit about their biases makes it easier to identify weak essays. But it's also worth arguing that no matter your biases, your writing is stronger when you rely on empirical evidence, rather than using generalizations/stereotypes that you assume the audience will agree are true.