I think any opposition to free speech, particularly as exercised in an election, is unseemly, but Hillary Clinton's attacks on the Supreme Court's Citizens United decision are particularly so.
Why? Well to understand, we have to remember what the Citizens United case actually was. Over time, the decision has been shorthanded as the one that allows free corporate spending in elections, but this was not actually the situation at hand in the case. I could probably find a better source, but I am lazy and the Wikipedia summary is fine for my purposes:
In the case, the conservative lobbying group Citizens United wanted to air a film critical of Hillary Clinton and to advertise the film during television broadcasts in apparent violation of the 2002 Bipartisan Campaign Reform Act (commonly known as the McCain–Feingold Act or "BCRA"). Section 203 of BCRA defined an "electioneering communication" as a broadcast, cable, or satellite communication that mentioned a candidate within 60 days of a general election or 30 days of a primary, and prohibited such expenditures by corporations and unions.
Yes, the Supreme Court generalized the decision to all corporations and unions (good for them) but the narrow issue in the case was whether an independent non-profit group could air a negative film about Hillary Clinton in the run-up to an election in which she was a candidate.
So when Hillary Clinton derides the Citizens United decision, she is arguing that the government should have used its powers to suppress a film critical of her personally. She is trying to protect herself from criticism.