I think it's safe to say that the United Federation of Planets does not engage in capital punishment anymore
Maybe they might want to reconsider this. Wouldn't it be much too dangerous to leave any Section 31 member alive?
Julian Bashir, for instance, is apparently considered to be a member of Section 31 by them, and has even undertaken missions upon being assigned one from Thirty-One; does that make him a member who deserves to be arrested and tried for treason? On the other hand, he's also a part of the Kirk cabal of anti-Thirty-One officers.
I don't count Bashir as a member, and never did. He was recruited against his will, and obviously did not agree with their ultimate goals. And as you say, he was part of the Kirk Cabal working against them. That leaves Bashir off the hook, as far as I'm concerned.
I'm sure he did. But that doesn't absolve him of blame. Unlike Bashir, I consider Ross a full member of Section 31 who should be held accountable for their crimes. It's just a pity that Sloan is already dead and unable to face a public trial and punishment.