The article suggests that you can do the opposite of that (use traits of the individual to reasonably accurately infer that they're male or female).

The parent's concern is that, given you know someone is male or female, you will make further assumptions about them based on their group membership rather than their individual traits, something that is not supported by the article.

> I am a strong believer that individual differences are more important than sex differences.

But the only case where you would rely on group membership is if the individual traits are unknown. Obviously generalization will never be as accurate as individual knowledge. Why would anybody be worried that people would act otherwise?

Assuming things about individuals based on group membership is a key part of racism, sexism, etc. Why would anybody be worried? Because people do it all the time.

Stereotypes exist because there are statistical patterns in groups of people. Those stereotypes are useful cognitive tools while they remain accurate. It certainly isn't fair to people in those groups who don't fit the stereotype, but as long as the stereotype accurately describes the majority, there's nothing to be done about it.

Would you run up to a lion or a tiger in the wild and try to hug and kiss it? I'm guessing you have a stereotype of big cats as dangerous predators, and you'd steer well clear, even though there are countless friendly lions and tigers in captivity that have never hurt anyone.

Are you saying that with a high accuracy, you'd feel comfortable treating an individual according to their group?

I don't want to appear too argumentative; it's just not exactly clear what you mean when you write

> .. difference here is strong enough that you can do that

Do you not do that? When you are first approaching someone you don't know, do you not take their expressed gender into account in how you make the initial greeting? Would you offer a woman the exact same handshake you'd offer a guy?

How would you approach someone who doesn't fit the norms - for example a male bodybuilder in drag? Does your brain hiccup for a moment when considering how to greet them? Mine does.

I'm sure I do act a little differently, but I try very hard not to.

Especially if I work with them or have some influence over their future.