Attorney James Bopp writes an interesting article titled "Silencing Criticism-The history of sham arguments for McCain-Feingold." in the National Review.
It is my opinion that McCain-Feingold, otherwise known as the Incumbent Protection Act, is solely designed to stifle criticism, keep incumbents in office, keep the Republicans and Democrats in power, and keep upstarts like the Libertarian Party at bay.
How do you start a "loyal opposition" if the bureaucratic compliance costs keep most people away and are hugely expensive? Who really wants to go to jail for the political crimes contained within McCain-Feingold and other similar Incumbent Protection Acts?
How do you stay in power? - make it prohibitively expensive for new people to get involved, make it bureaucratically complex, and make the risk of jail for violation of unclear laws a real possibility. McCain-Feingold is very successful at this, which I believe was the desired result by most lawmakers who voted for it.