I think the intention, despite the title, is not to say that GUIs are harmful. I think more what he's saying (especially in the closing paragraphs) is that both

I think the intention, despite the title, is not to say that GUIs are harmful. I think more what he's saying (especially in the closing paragraphs) is that both a GUI and CLI need to co-exist because they target different groups. He's against bundling a GUI as the only method of interface to a given program, but rather wants the application to be open to both. Not agreeing or disagreeing with his viewpoint, just summarising.