Section 31 were created as the bad guys! Genocidal maniacs who Sisko and crew fought against every step of the way.
And I don’t use the phrase “genocidal maniacs” lightly, but they were literally xenocidal and Sloane was, as a spy, less of an Ian Fleming James Bond type and more of a John le Carré type—an actual maniac in the piece of human wreckage who’s been turned violent and crazy by the stress of war.
(I really wish his end had come at Sisko’s hands, and involved contrasting Sisko’s actions in Pale Moonlight with Sloan and 31’s degeneration in to xenophobic crimes of extermination, and how both shared the same origin but ended up in very different places.