For me, this article was thought-provoking throughout, but there was a very deeply-buried lede as well: in the linked interview with Maria Klawe[1], all the way at the bottom, where she mentions separating the 101-level CS class by previous programming experience. I think that an exceedingly large portion of the barriers to entry faced by students trying to enter the field is due to the disparity in experience, which masquerades as a disparity in aptitude. That disparity turns into a large barrier to entry, due to both self-selection on the part of the students (feeling intimidated and outclassed), and also the issues being discussed in this article about being written-off as no good by the professor.

There may, perhaps, also be an inherent aptitude component as well. I still sort of think that there probably is. But we still shouldn't confuse that with what's really going on in the intro classes. Some kids that have the aptitude, and still have the potential to become exceedingly competent, should not be weeded out just because they didn't have the good fortune to be exposed to CS before college.

[1] Full disclosure: HMC alumn