How did the Citizens United majority use the idea of a marketplace of ideas?

In the majority opinion for Citizens United v. Federal Election Commission, the U.S. Supreme Court utilized the concept of a "marketplace of ideas" to argue against government restrictions on political speech by corporations and unions.12

The majority, led by Justice Anthony Kennedy, contended that suppressing political speech from these entities interferes with the marketplace of ideas by preventing their "voices and viewpoints" from reaching the public. The court reasoned that such speech is essential for advising voters on which persons or entities may be hostile to their interests. By invalidating bans on independent corporate expenditures, the court asserted that the government cannot assign different free-speech rights to speakers based on their identity, as doing so would distort the open exchange of information necessary for a functioning democracy.2

Ultimately, the court concluded that no sufficient governmental interest—such as preventing corruption or protecting shareholders—justified limiting this speech, as the marketplace of ideas is best served by allowing a wide range of participants to contribute to the political discourse.2