I'm actually somewhat iffy on this.
This gives Disc a lot of leeway by not defining either what makes a site adversarial or which sites are adversarial.
A broad definition makes it easier on Disc, no doubt, but it's possibly ripe for abuse, and is certainly entirely subjective, as presented.
Additionally, this lack of a clear definition would make it difficult for users to know if a site fits the bill, either as a member of that site, or as a user reporting a potential rule infraction.
To us, it may seem obvious, but certainly not to everyone.
At the very least I think it would prove useful to have a list (descriptive not prescriptive) of sites which fit this bill and/or of attributes that would make a site fit this bill.
Specifically this rule will apply most often to RPC users at the moment.
Now I have no love lost on RPC. As a community they facilitate bigotry in many forms, and I'd be happy to see it shrivel up and die.
However, loathe as I am to admit it, we have several users who have for some time been consistently rule abiding members of the SCP wiki and/or Discord and have not at all engaged in bigotry, to my knowledge, here or elsewhere and who are active or inactive members of RPC.
Is their mere membership on that site enough to net them a potentially permanent ban? I'm not sure.
There's something to be said for tacit endorsement of bigotry just by being in the community, sure, but it's worth noting that certain INT branches of SCP have positive relationships with INT branches of RPC. And while a positive relationship doesn't apply to RPC-EN at all, my point is that those sites being affiliated with RPC in some way likely shouldn't net their users an automatic ban. At least, I don't think so. And with how wide this policy is, it's difficult to guess from a non-Disc point of view, whether or not this would be the case.
We have/have had several members of the SCP Discord with current or past RPC affiliation who have been fine to have around and have never, to my knowledge, engaged in bigoted behavior or language either in SCP or RPC (or elsewhere that I know of).
Now I'm not about to shed a tear if all RPC members (especially members of their staff) get permanently banned from the SCP wiki. Fuck RPC.
But I do think this is a very wide, very subjective net that would be cast, and it will catch people who haven't overtly behaved in any wrong way.
We should be careful about that.
(I recognize this applies to one of our current reasons for application denial, treat this as a commentary on that current rule as well.)