The 5-4 majority of the Supreme Court found that a major part of the federal campaign finance law infringed on the right of corporations to speak in political campaigns. The court's decision levels a playing field that was statutorily tilted toward certain mainstream media corporations who were exempted from this corporate prohibition even though they were big, profitable corporations like News Corp, The New York Times and the Washington Post. News and other media outlets were free to support or attack a candidate while all others had to remain silent. This court ruling overturned a law that didn't just prohibit some speech, it made exercising the right to speak difficult. The overturned law applied to 33 kinds of political speech. If the the FEC ruled that one didn't comply, there was potential civil and criminal liability.
The very notion that corporations are not covered by the First Amendment because they are not persons is short-sighted at best. Corporations are collections of individuals. To quote Justice Antonin Scalia: "To exclude or impede corporate speech is to muzzle the principal agents of the modern free economy. We should celebrate rather than condemn the addition of this speech to the public debate."