What concerns did Justice John Paul Stevens raise in his Citizens United dissent?

In his dissent in Citizens United v. Federal Election Commission, Justice John Paul Stevens argued that the majority’s ruling threatened the integrity of elected institutions. He raised several key concerns:1

• Disregard for Precedent: Stevens contended that the Court ignored the principle of stare decisis and used a "question-begging and ad hoc" rationale to address the facial constitutionality of the law.1
• Marketplace of Ideas: He argued that the majority misunderstood the state’s interest in preventing corporate domination of political speech, noting that such influence could impoverish rather than enrich the "marketplace of ideas".1
• Corruption and Democracy: Stevens criticized the Court’s definition of corruption as being limited to quid pro quo exchanges, calling it "simplistic and naive." He also argued that the majority overestimated the ability of "corporate democracy" to protect shareholders from having their funds used for political speech they oppose.1

Ultimately, Stevens warned that the Court’s approach would hinder the ability of citizens and government bodies to protect the electoral process from corporate influence.1