to quote Lord Acton, "Absolute power corrupts absolutely." The paternalism (separately) of the Second Foundation and Daneel mark them, in my eyes, as the villains of the overall saga.
I dunno. Studies show that whether people use power for good or ill is contingent on their pre-existing character, so that only the people predisposed to corruption would use power corruptly. Stories like "Evidence" argue that a Three Laws robot is intrinsically incapable of corruption, since they would always put the good of others (or in Daneel's case, the good of humanity as a whole) over their own self-interest.
Although one could fairly argue that a Zeroth-Law willingness to sacrifice individuals for the sake of some statistically calculated "greater good" for humanity in the long term is a form of corruption, particularly if one individual takes that responsibility onto themself without any checks on their power or judgment. That was what Acton was really writing against, the existence of offices or institutions that are presumed to be infallible and thus have no restrictions on their authority.
But really, the overall politics of the Foundation books are problematical, since they basically take it as a given that an authoritarian empire is necessary for the good of humanity, and democracy doesn't even seem to be considered as an option.