Precisely..........Marcus and Sloan do not view themselves as 'evil'. They believe they are doing what is necessary to protect the Federation. But how they do that, how that manifests, is by choosing courses of action which seem to run contrary to the outward presentation of Federation values and ideals.
It's covert foreign policy.
And the lessons of foreign policy do not get learned (going back decades, centuries even in some cases) and repeat themselves. This is why Kirk's lesson remains of value. His speech may be relatively simple sounding but the simple lessons are the ones that can be easiest to forget and constantly need to be relearned (in drama as in life...........we all forget and have to be reminded). To regain a measure of focus when it's easy to lose sight of it.
This applies retrospectively. Admirals in Trek seem a generally conniving crowd. They don't seem to learn their lessons at all. Dougherty follows Pressman follows Nechyev follows Jameson follows many others. All of whom chose to take a path contrary to what the Federation is supposed to be about. All their actions cost lives in and outwith Starfleet. Not all of them seemed to pay a price and none of their actions deterred other Admirals from their own machinations.
We don't even know what happened in Starfleet when the likes of Pressman and Dougherty were exposed. In fact.......to what degree were they even exposed?
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist