Aside from the (in my opinion) craziness of the decision itself, what I've noticed in the commentary is a striking inability of commenters to distinguish between the commercial and the government (guardian) realm.
Most clearly, here is Glenn Greenwald,
"So I'll ask again -- of you and anyone who claims that since corporations are not persons, they have no rights under the Constitution:
Do you believe the FBI has the right to enter and search the offices of the ACLU without probable cause or warrants, and seize whatever they want?
Do they have the right to do that to the offices of labor unions?
How about your local business on the corner which is incorporated?
The only thing stopping them from doing this is the Fourth Amendment. If you believe that corporations have no constitutional rights because they're not persons, what possible objections could you voice if Congress empowered the FBI to do these things?
Can they seize the property (the buildings and cars and bank accounts) of those entities without due process or just compensation? If you believe that corporations have no Constitutional rights, what possible constitutional objections could you have to such laws and actions?
Could Congress pass a law tomorrow providing that any corporation - including non-profit advocacy groups -- which criticize American wars shall be fined $100,000 for each criticism? What possible constitutional objection could you have to that?"
Notice that all the question Greenwald asks relate to commercial matters. He doesn't ask if corporations should be eligible to vote, to hold office, to serve as judges, or to lead the army.
Or take Julian Sanchez,
Why is it that so many people who clearly do think books and magazines and talk radio shows enjoy unambiguous constitutional protection, despite being corporate funded or operated, are simultaneously absolutely sure that paid broadcast spots are in an utterly different category? ... My hunch is that it has something to do with the imagined audience.
No, it's because the first group falls under the category of art, whereas commercials, much like corporations, are under the category of commercial activity - which should be kept separate from the political world as much as possible.
Very rarely in what I've read on the case (and then only in the comments to posts) has anyone made the simple point that a corporation is a commercial entity, created for a solely commercial purpose. Therefore it makes perfect sense that this commercial entity should be kept out of the political world as much as possible. Yes, a corporation should have property rights, and be protected from theft, but that doesn't mean it should have full political rights as well, there's no slippery slope and there is a clear line to be drawn.
Even if people haven't read and been persuaded by Jane Jacobs' argument that systematic corruption is the inevitable result of mixing commerce and politics, I feel that we used to have a stronger intuitive moral sense about these things.
Update: Here's an honourable exception, Justin Fox.