Don't ban the criticism of politicians

Why do people have so much trouble understanding that the Citizens United ruling did not allow unlimited campaign contributions, but ended legal bans on the criticism of politicians near election time?

Al Franken is just one of 49 cosponsors of a senate bill that would reverse the Citizens United ruling. That's 47 Democrats and one crypto-Democrat, Angus King of Maine (Officially an Independent). The basic argument is that corporations and unions should not be able to broadcast ads criticizing candidates for office near an election or primary because those ads function as ipso de facto campaign ads for the benefit of other candidates, and that could be used to circumnavigate campaign donation limits.

Well yes, that much is true, and while people can disagree with the legitimacy of campaign donation limitations, even people who want strict campaign limits have to admit there is something sinister about a law that would make it illegal for a corporation like Nintendo from airing an ad criticizing a candidate who wants to ban all video games, or ban similar ads from the ACLU, NRA or Planned Parenthood.

That's clearly a violation of free speech.

Franken said the Citizens United ruling is "One of the worst decisions in the history of the Supreme Court." Does he actually mean that, and understand what the ruling was about, or is he just playing to the ignorance of his base?