I have enjoyed the answers everyone have given. Really a case can be made either way. Sloan was not impulsive however, he showed great patience.
To me Sloan on screen completely lacks emotion or guilt. This can't be said for any of the other characters on DS9, all who have committed acts of homicide(except Jake?).
All the great captains of the Star Trek series have been shown to be weighed down by the the pros and cons of following or breaking orders/laws in the resolution of a plot problem. What evidence of ethical paralysis did Sloan ever show?
Well, you remember the moment at the very end of "Inter Arna..."?
http://www.youtube.com/watch?v=5V3EF-nzC2Q
Look carefully when he says to Bashir, "You did the right thing." From that point on, until Bashir replies, Sloan actually looks sad. Thus, when he says the line about sleeping at night...I wonder if he is implying the feeling of guilt on his part.
Who is Sloan accountable to? If he is a big part of the organizational strength of Section 31 then he is accountable to himself not others.
I've theorized that Sloan is one of many directors of certain "divisions" of Section 31. They each have absolute control of their divisions, and they have deals in place that no director may interfere with another's division, for fear of reprisal.
Still, they all hold each other basically accountable. If it is proven that a director is not working in the best interests of the Federation...
Did Sloan ever think that his rationalizations were more valid than others? I mean if I decided to start murdering people and altering the makeup of the Romulan government I might feel a little bad if those choices enabled Shinzon to rise to power in his quest to destroy Earth.
Frankly, Shinzon would have carried out the coup regardless. I doubt Sloan's actions had anything to do with it.