This last bit, which you dismiss, is my point. Corporations have leaders which are elected, and their actions are subject to review by stakeholders. So why shouldn't they have similar rights?
It might be useful to separate "business rights" from "speech rights", but there should be a way for people to speak as a group. Class-action lawsuits, for example, allow a lot of people to be represented in court without personally being involved in the legal proceedings. Political institutions speak on behalf of significant chunks of the population on a regular basis.
And how would a corporation publish a prospectus without the right to speak? If prospectus contains lies, would you hold the individual who wrote it accountable? That defeats some of the protections a corporation provides, and means the stakeholders get a lot less money if they sue.
The problem, is that isn't true. In practice, save via a very expensive proxy fight, shareholders have almost no actual voice within most corporations.
Only the deeply cynical could hold that up as an analogue to democratic government and even they wouldn't say it was a positive state of affairs worth emulating.
there should be a way for people to speak as a group
There is. You just couldn't speak, as a group, through a shell entity that has its own inalienable right to free speech.
Not having freedom of speech equivalent to individuals doesn't imply a complete re-write of corporate law. It simply means that congress can (constitutionally) make laws abridging and regulating corporate speech.
No-one's proposing a change to how we handle corporate fraud and responsibility. I fail to see how the right to free political speech has any bearing on those areas.
An 'expensive proxy fight' is still cheaper than the campaigns required to reliably influence an elected government.
What's more, shareholders have many other options for influence. They can buy additional shares directly. They can 'exit' -- move their money elsewhere, empowering an alternate organization that does represent them.
In the comparison between shareholders and voters, it's not clear to me that it's shareholders who have less influence.
"And how would a corporation publish a prospectus without the right to speak?"
Bear in mind that the corporation is free to do anything that isn't prohibited. What we're talking about here is whether a corporation can avoid a legitimately-enacted regulation by claiming immunity based on a fundamental human right. Corporations can go right on publishing prospecti. And corporate officers are immune from liability (except in certain extreme cases of wrongdoing).
This will be the case as long as government (ie, we the people) decide it's in our best interests. If for some reason government (again, us) decide it's no longer in our best interest, then we can prohibit publishing a propectus without fear of violating some imaginary entity's rights. We can already prohibit the formation of corporations entirely (ie, withdraw the privilege of immunity that corporate officers enjoy), so it is simply silly to say that we can't regulate them on some bizarre human rights claim.
The reason this comes up in the election context is that corporations want to double dip: all of their personnel can give to the individual limit, then give again in the name of the imaginary entity. It's a shell game, and it's good to see Sotomayor is smart enough to see it.
It might be useful to separate "business rights" from "speech rights", but there should be a way for people to speak as a group. Class-action lawsuits, for example, allow a lot of people to be represented in court without personally being involved in the legal proceedings. Political institutions speak on behalf of significant chunks of the population on a regular basis.
And how would a corporation publish a prospectus without the right to speak? If prospectus contains lies, would you hold the individual who wrote it accountable? That defeats some of the protections a corporation provides, and means the stakeholders get a lot less money if they sue.