shein, I don’t think Health is disagreeing with the Chofetz Chaim. I think he is simply saying that such a “mitzvah” wouldn’t apply to Mason, as he showed from aries’ post. And I think Health is right.
Now, about this ruling of the Chofetz Chaim, I have a question. Instead of spending the time speaking badly about an influential “OTD” person to prevent others from following, wouldn’t it be more beneficial to spend that time trying to help such a person find their way back to Judaism? And even if that would be impossible, and someone is being influenced by such a person, wouldn’t it be better to show why such a lifestyle would be unsatisfactory instead of speaking negatively about the person himself? Also, if one gets accustomed to speaking badly about people, even in situations where it may be a “mitzvah”, it can G-d forbid possibly lead to making them more comfortable with speaking badly about people when it definitely isn’t a miztvah.