I am a full time trade union official and legal adviser (employed by the union, not elected). I have done this work, and similar, for about 20 years.
I don't agree that all HR people are bad, or even that the HR function is bad. In fact, I often recommend managers to get their HR folks involved, when they are considering what they should do with regard to people they manage.
Of course there are some bad HR folks. There are bad trade unionists, too.
Overall, in my considered view, organisations who employ a properly trained HR specialist are able to provide a better service to their staff and their managers (and, usually, are more willing to work with trade unions) than those without.
So there!