Honestly, I feel you're snowballing something that is really a non-issue.
Ian (and rest of SMS staff), as disheartening as it is to see someone bashing you and using baseless claims as the reason for it, you might be doing yourselves an even bigger disservice by requesting things like moderation on a thread on a fansite. I mean, yes, the thread appeared on other sites. Big. deal.
Seriously, it has as much relevance as you want to give it, even if it hits the New York Times headlines, as long as the part being accused here (you) can defend itself through the proper channels if it even gets THAT far (PR) there's no loss.
pCars has a large fan base, especially for a game that's still in development and requires a fee to access the client, and there's obviously going to be disgruntled users, trolls, and so on. It is disheartening. It sucks. And it's even offensive when you see those people bash the work of the guys working around you day and night to deliver the best product you can. I know that feeling. I've been on this industry for long enough to understand that. But in the long run, this is far more damaging than a million fansites speaking about a user that was banned for no reason. Heck, this thread on itself could be used to craft news bashing you, based on what has happened here, and make wild accusations backed by the posts here. It's seriously gone too far. Way too far. I don't know if you have a Community Manager in your team. But if you don't, please, consider hiring one or having someone onboard that can help you with that. On this particular case, you've missed a few chances to make yourself as a company look good and get rid of whatever you considered damaging to yourselves.
Also, that screenshot showing the "No reason specified" (assuming is real) is a serious mistake. I mean, not the ban, I could care less about why anyone was banned. But the fact that no reason was provided for it. It's just not good practice because it leads to things like this.
Having said that, in the other hand. RD staff. Yes, you are volunteers. Yes, you are simracers. Yes, you don't necessarily have to have community management experience. And yes, you're owners of your own words. But keep in mind that you're also part of what shapes the RD forums. Your opinions are usually well considered by the rest of the community, and they can very well turn into something that leads people to say "hey, if they are saying X, it must be X!".
Finally, RD is one of the biggest simracing fansites, afaik. So, I'd say for SMS it's on the best of its interests to actually have a good relationship with them (and any fansite that wants to devote their time to pCars in any shape or form, really) and at the same time, is just as interesting for RD to have that same good relationship with SMS. Why? Because eventually, the game will be released, and it'd be a shame if any new users that are brought to the genre by the game, don't get to know RD because this just snowballed into something crazy.
A parting thought: Ian mentioned 73000 members (correct me if I'm wrong). Let's put this number into the proper perspective for everyone. At most, of those 73000, I'd venture to say than 7300 might be invested enough into the game to go on other forums than WMD (that is your hardcore audience, generally speaking). Of those 7300, at most, how many of them might be on RD? 50%? (and I'm probably being too generous).
Fastforward to the release of pCars. Let's actually think that the game does well (I really hope so) and sells, I don't know, 2m units combined.
Of 2.000.000 players, at most, 3600 saw this one discussion in the alpha stages of the game were someone claimed he was banned for no reason. That's a 0.0018% of your playerbase. Even if you want to assume that the 73k members saw it, it's a 0,0365% of your playerbase. Which amounts to... nothing (almost).
So my question to both sides would be... Seriously? This one thing warrants effin' up all the benefits you can mutually bring to the table?
