Why did Justice Stevens criticize the majority’s understanding of corporate democracy?

In the case of Citizens United v. Federal Election Commission, the Supreme Court majority argued that the interests of shareholders regarding corporate political spending were adequately protected by the institutions of "corporate democracy."1

In his dissenting opinion, Justice John Paul Stevens strongly criticized this perspective, arguing that the majority’s reliance on the concept of corporate democracy was fundamentally flawed. He contended that the court’s notion of corporate democracy greatly overestimated the actual power that shareholders possess to influence corporate actions. Specifically, Stevens pointed out that shareholders lack sufficient practical ability to effectively vote on these matters or to successfully bring derivative suits against corporate officers to challenge political expenditures with which they disagree.2