The basic principle of the article is good. We should try to keep calm and use our heads. But in any creative process I would expect to hear a few curses and maybe even see people in a bad mood for a few days. That's fine as long as people still get on with it and don't behave like an asshole to those next to them. Creativity is a struggle. If he sees people who say something negative about the client as "poisoning the design process" then I think he has gone from giving some good advice to a kind of intolerance that's just not very practical.