Citizen's United (the case) held that any government restriction on political spending was presumptively illegal and in violation of the first amendment. That is exactly my point. It was NOT a narrow ruling tailored toward the needs of PACs trying to avoid censorship. It was a extremely broad ruling throwing out the whole concept of campaign finance regulation.

This is a common and misleading description. I encourage you to read the decision and at least part of Stevens's dissent (which is twice as long as the decision itself). I know it's a lot of pages, but it's got big fat margins.

Now.

(Reposting a comment I made elsewhere)

Before Citizens United, any US majority-owned corporation or union was allowed to make political contributions from a segregated fund. The money in that fund could only come from employees and shareholders. This was, in decades of previous legislation and case law, considered sufficient to protect the 1st Amendment interests of associations of individuals. They can pool their money together for political purposes, put they can't pool it with other people's money.

Before the ruling, Citizens United was allowed to spend money on political activity. They were allowed to spend money on political activity close to an election. They were allowed to spend money, close to an election, to broadcast issue-based political advertisement (e.g., for or against a ballot initiative) on TV. They were allowed to spend money distributing their documentary in any way other than broadcasting it on TV. They could show it in theaters. They could put it on the internet. They could print DVDs and mail them out. They could distribute it to PACs and campaigns for them to spend their own money distributing it, including broadcasting by on TV. They could pay money, close to an election, from a segregated fund, to broadcast their documentary on TV. All they weren't allowed to do was spend money, close to an election, on broadcasting something expressing views for or against a political candidate, on television or radio, to an audience of at least 50,000, close to the election.

Corporations were not banned from electioneering before Citizens United. They were restricted. The laws imposing those restrictions went back until at least the early 1900s. There was a century of case law find some such restrictions constitutional. There was a decision in 2003, just 7 years before Citizens United, upholding the very restrictions that CU struck down. The majority's argument rested on the idea that no "identity-based" restrictions on 1st-Amendment rights are constitutional. But there are such restrictions, e.g. against prisoners, students, and employees of the executive branch. These restrictions remain in place today. The majority invented a 1st-Amendment principle and then selectively applied it to corporations. They did so with no fact-finding in the record of the case on whether the provisions they struck down actually chilled free speech. Fact-finding that the government wanted to do before Citizens United (the organization) dropped the issue.

The majority in Citizens United flipped the table on decades of election law that had survived scrutiny several times before without even claiming that any circumstances had changed. They did it solely because they didn't like the outcome. And they bent over backwards to do it.