He's pointing out that you can use your argument as a counter-argument to yourself. As a result, your point is more or less moot, and all that remains is an appeal to cognitive bias (women enter these fields for "fun" or to find a husband, while men do it for the "real reasons" or something like that [1])

[1] The beauty of your vagueness is that it allows someone to inject whatever they believe is the "real cause" of the problem in the United States, perfectly allowing them to project their own bias upon your post as well. It also makes it difficult for someone else to counter it since they're not entirely sure what you're trying to say at all. An intriguing approach I must say.

I've had dozens of Iranian friends, most of them women engineers.

All of them in it for the love of science and engineering.