The group seems a bit more insidious now. http://blogjob.com/oneangrygamer/2014/10/gamergate-destructoid-corruption-and-ruined-careers/ Seems like that innocent group conspired to blacklist a journalist. Do still believe it is not a problem given what it has been used for?
As for the GameJournoPros group involvement, Neiro approached the group asking for advice on how to handle the situation, and the group provided advice. That is the group working as intended. In his post, Neiro was very clearly learning toward firing him anyway, and as your link corroborates, many of the responses were telling him that there's probably a reason he has the gut feeling and should follow it. Common advice was also to consult legal counsel, which is pretty standard advice in any firing situation. This is not conspiring, this is one professional asking advice on a delicate situation from their peers.
The second GameJournoPros involvement was when North posted in the group that Pinsof was trying to contact editors for work again. If that linked article had any commitment to honesty, it would have also shown that past the joke responses to North were responses that they already weren't planning to work with him due to his prior irresponsible ethical breach, or people saying they forgot about that situation and thanking for the heads up about a freelancer of questionable ethics. One of the other functions that the group serves is for editors to share with other editors which freelancers are good/bad to work with. This is not conspiring either. It was never the group coming together saying "nobody hire this guy" it was bunch of individual editors saying "Oh god, him again? I wasn't going to hire that guy anyway because of how he conducted himself previously." But to your question, no, I do not think it is a problem for the group to be used to inform editors of writers who have low ethical standards in their writing. He blacklisted himself through his actions, not because the group conspired to make him some untouchable writer.
Now, I cannot speak to how Destructoid and its staff conducted itself outside of the group in actually firing him, since I am not a part of that staff. I will say though that I have heard some pretty bad horror stories about working with Destructoid, and that article brings up Holly Green whose experience there is a very good example of editors at that publication conducting themselves in a grossly unprofessional way. But that is her story to tell, not mine to tell for her, and I condemn anyone who tries to pressure her to tell it against her will.