I think you misread that paragraph. He does not seem to be writing only about programmers, but about everyone that a startup might need to hire. Read this again:

"Shapiro, who has blogged in the past about sexism in the tech industry, notes that "it is a widely understood truth that the single biggest challenge to a successful startup is attracting the right people. To literally handicap yourself by 50 percent is insanity." "

His point, as I understand it, is that if a startup has a bro culture, then women won't want to work there. That includes women in marketing, women in sales, women in HR, women as project managers, etc.

And yes, it is a serious issue. Even if you accept the (highly questionable) thesis that only men like to program, are you willing to argue that a growing company will never need women in marketing, sales, HR, management, etc?

In that light, he is quite right when he says: "To literally handicap yourself by 50 percent is insanity."