I actually get where Maher, etc., are coming from when they say that going after their sponsors is an assault on their free speech rights.
No, they're not right on law, but what does it say about a society where the most valuable speech - speech that can reach millions of people - is pretty much controlled by private interests whose only concern is making money? It's our own little dystopia where the ability of a thought to make a rich person even richer is more important than that thought's ability to create change or shed some light on the truth.
This is because the listeners to Limbaugh's radio show or the TV audience of Maher's old ABC show aren't the customers. Maher and Limbaugh may have worked to build bigger audiences, but the product they're selling is the audience's attention, and their customers are the corporations buying ads.
When an advertiser pulls out of a show because of content, not viewership, people are reminded that the power is behind the curtain and they start to get upset. Advertisers policing content is an arbitrary limit on the ideas that people are allowed to hear.
Free speech is limited when that happens, but free speech was pretty much limited when some suits decided who to hire in the first place based on financial concerns instead of journalistic or artistic merits. That is, this free-speech denying system created Rush Limbaugh, and it can destroy him.
That doesn't mean it's the best system, and it doesn't mean that articles from Media Matters that say it's great that the free market is putting a higher price on some speech based on content don't sound creepy to people outside movement liberalism. We cringe at the thought that an unpopular but true idea can be suppressed because corporations don't like it, but we cheer on unpopular and untrue ideas being suppressed because of the free market (when did liberals start sounding like Ayn Rand?).
It raises an obvious question: is the free market the best way to distinguish between true and untrue ideas? What about distinguishing between harmful, beneficial, and benign ideas?
To put it another way: did the free market work all that well in ensuring that only people of deep knowledge and insight in foreign affairs and Iraqi politics got air time to discuss that invasion in 2002 and 2003?
All this points to collective control of some media outlets and a greater awareness that, while you don't pay money for a subscription to certain media outlets like MSNBC or Fox News, it doesn't mean that they're "free" in either sense of the word.
At least when you pay a subscription fee, you know that you're the customer. And if we decided in the US that we collectively owned the airwaves because they're a natural resource, then perhaps we develop other systems of determining who gets air time and who doesn't.
Because the "throw daily tantrums and bark whatever pops into your head to get attention, until you call someone a slur and then you get fired" system we have now isn't making anyone smarter.