There are times when HR is the proper way to go. Obviously, this manager isn't just making this individual's life miserable. For the sake of the company, he needs to be dealt with one way or the other. Otherwise, he will drive out all the talent in his particular area.
Getting HR involved in situations like this doesn't result in unionization. I would say that lack of response from the company in resolving the situation COULD do so.
Especially in this economy, not everyone can just hop from job to job when there is a problem boss. Good for you if you have such specialized and in-demand skills that you can do so. But most can't.
√ sexual harassment
√ physical harassment
√ drug use
…
improper use of bcc by management (find a new job)