How to ensure this place will not become toxic, as some other social media platforms can be?
By being nice to each others. None of the original users of Sublevel/Subcafe had any problems on this platform up to its closure 2y ago. Since its rebirth, it seems it is finally getting a bit more of the attention it deserves. And inevitably, it comes w/ some of the new people directly accusing the platform of racism w/o knowing it never has been the case. How would they know? Even if they knew, they absolutely don't care anyway. Only time will tell how Subreply will evolve.
What are the racism accusations about?
That's the point, there is no good reason. The platform is apparently racist just by saying that it is not for some people. The same people who have already posted things like "all white people are the problem" or else, while I'm sure no one here as yet posted racist things like "blacks are this and that", out of the blue. But you are still racist if you engage in civil discussion. Go figure. Hopefully, no reshare or ranking here, so it is rapidly lost in the end. Sensible?