Plausible deniability is a velvety layer of insulation between the people who carry out the acts and the person elected or appointed to take responsibility. By the time the denials, obfuscations, delays, hand-wiping, shoulder-shrugging and tied-hands miming is done, the guilty parties are gone and the trail is so convoluted that it becomes very difficult to prove that the leader was anything more than ignorant of what went on. That feigned ignorance, in turn, provides lots of grist for righteous indignation about unauthorized overreach by lone rogue actors, partisan charges that the opposition is trying to muckrake and blah blah blah.
Political abstractions may be leaky, but they hold water long enough to get the job done.
Right but if you create a layer of plausible deniability you are still responsible for the consequences. If the head honcho says "Yeah you can kill the people on the list I haven't seen" I don't understand why seeing the list is a requirement for them to be responsible. Otherwise, what is the point of them authorising the act? May as well not bother.
It's the difference between being held responsible (politically, maybe, eventually) for a botched policy execution and being held responsible legally for a criminal act. Plausible deniability shields you from the former for long enough that the political news cycle has stopped caring and shields you almost absolutely from the latter.
Political abstractions may be leaky, but they hold water long enough to get the job done.