If the Supremes rule in favor of Citizens United, as seems likely by the analysis on the wiki, it means that corporations have the right to broadcast propaganda to influence elections. Imagine during the 2012 elections seeing a dozen or so anti-Obama broadcasts, in various disguses (news, infomercial, documentary), funded by corporate interests without disclosure, posing as "grassroots." Massive propaganda compaigns would diminish any voice a public might have.
Moreover, the brief goes further, urging the Court to strike down a 1990 decision — Austin v. Michigan State Chamber of Commerce — that upheld a compelling interest for the government in regulating expression by corporations who may be very wealthy. That decision, it contended, “is flatly at odds with the well-established principle that First Amendment protection does not depend upon the identity of the speaker.”You have a lot of voice if you are a wealthy corporation with billions to spend to influence an outcome that may not have the public interest in mind. The Bill of Rights was argued for ratification to grant fundamental human liberties, not for shady entities to run propaganda campaigns.
As Noam Chomsky observed, "He who owns the media controls the mind of the public." It is clear now, if not before, that the conservatives on the court who want to take up this issue to give corporations (global in scope) control of the elections are the real judicial activists. If you think the corporate interest money that's pouring into killing health care reform is stunning, consider what's at stake in the next elections. What's at stake is the nature of our elected officials, whether they are working for corporate interests or the public. Good luck democracy.