Feingold was part of the McCain-Feingold campaign finance reform act, which I would say makes him a limiter of free speech.
I would argue that you are falling into the same mistake the Supreme Court has made repeatedly, equating money with free speech. Money is not speech, money is power. Misuse of this monetary power is what has seriously corrupted the US political process.
While McCain-Feingold may not have been perfect, it was a step in the right direction to limit the influence of money on the US political system. It is one of the great ironies in that international election observers would consider the US campaign contribution system highly corrupt if it were replicated in any election they were monitoring.