IMHO the 60% remaining private is the gruesome details of perversion, torture etc.
Not the texts perhaps discussing or implying harm to POTUS/family.
Could be, but he’s also implied that some things would be kept hidden because they would cause social chaos and breakdown (i.e. governments could fall, etc.). In this instance he suggests that revealing these texts could delegitimize the FBI to such an extent that they could jeapordize any case prosecuted by the FBI over the past number of years (i.e. their legality could be challenged in court), regardless of their being directly related to POTUS and 2016 election. Chaos indeed. Anyway, moot point since it appears they decided to release them anyway.