Citizens United involved neither a big corporation nor an instance of anyone "bribing" a candidate.  You haven't read the case, have you?  Citizens United, a non-profit, wanted to show a documentary critical of Hillary Clinton, and to advertise the film during TV broadcasts.  McCain-Feingold prohibited any such speech within 60 days of an election.  Given the First Amendment ("Congress shall make no law . . .  abridging the freedom of speech"), Scalia's position was not only reasonable but right.  And it certainly wasn't an instance of him unreasonably ruling in favor of a "big corporation."  You really haven't a clue about what you're talking about.