Shavy Also, the player who has legacy bans shouldn't appear over the flagged page if the player is already unbanned from the league in which clan he is at.
Let's table this part as a separate issue. So this proposal is only to change the policy where a clan is marked as BL if it is official in one league and BL by another.
I disagree with the FWA-specific reasoning. FWA has good reasons to ban clans (and player bans are irrelevant to this proposal). The special privileges we extended to FWA for their isolation needs on cc do not have anything to do with clan associations, too, so in this matter they're the same as any other league.
So, in my opinion, the chief question here is, which has the most impact (weighted by the probability it happens) if people don't read the league extra text: mistaking your opponent for an inter league match when they're actually sync stalking your league, or mistaking your opponent for a blacklisted clan when they're actually officially in your league.
I think this difference is much more significant than which clans appear on the clan list page, since only administration really uses that page, so something that affects clan leaders' use of cc affects war farming many times as much. If clans look at the league status of their opponent for a brief moment, and don't read the extra text, I think we would rather take the mistake that prevents sync stalking, rather than one that allows it, even if it means extra-negligent clans may accidentally switch to war bases against a league match. I believe all leagues have policies that say to contact an admin on BL matches, so either way, the clan must be negligent twice to make this mistake.
Alternatively, this all can be mitigated if we adopt a policy to not take blacklisted clans of other leagues. But, with FWA's non-cooperativity on information sharing for their blacklists, that may be impossible.