Greenwald is making the Libertarian defense of this ruling arguing that money is, in fact, speech, and he's being, IMO, absolutist about the First Amendment. No constitutional right is an absolute, and it's one thing to defend a principle; it's another to go rigidly fundamentalist about it.
So again, no value, no matter how sacred, is absolute, and when it comes to "liberty" rights, they have to be held in a kind of tension with "equality" rights. It's one thing to say that we're all free to say our piece; it's another to say that people with enormous resources should be allowed to buy a monster megaphone to say theirs. It basically reinforces the idea that some people are more free than others, and that should never be true in the political sphere, where, I would argue, equality should be the dominant principle. (Liberty, the way I think about it, is the dominant principle in the cultural sphere, not the political or economic spheres, but that's argument for another day.)
If money equals speech, the power of the rich to buy a greater amount of speech creates a fundamental inequality problem, and it diminishes the free speech of citizens with modest means. There's an injury there that ordinary citizens should be able to seek a remedy for, but after today's ruling it would seem impossible to do so.
To argue that laws like McCain-Feingold were ineffective is one thing, but to ban forevermore, as a matter of constitutional precedent, any attempt to limit money spent to influence events in the political sphere by the mega-wealthy is horrifyingly undemocratic. It's another hard slap at the equality principle, which lately always seems to lose in its tug-'o-war with the liberty principle.
Look, I get there are problems, as for instance with media corporations' ability to use their megaphones in a way that other non-media corporations cannot, but the remedy is not to empower other corporations, but rather to get the media out of the hands of profit-driven corporations. We need to find a way empower, through subsidies, a more diverse, robust, and non-profit press. A subsidized, non-profit free press sector would lead to a healthier exercise of the First Amendment than our current corporate-owned system. But that, too, is an argument for another day.