Questions, questions... But the answer isn't limiting the 'free speech' of corporations.

Indeed not. The real answer is that our notion of good corporate governance -- and of corporate citizenship -- is broken, and we need to come up with a better model for running private enterprises within a larger society; one that doesn't reward sociopathic behaviour and allow them to externalize all liabilities to the public sector while avoiding paying the taxes that go towards handling those liabilities.

Shorter version: the most highly evolved vehicle of modern capitalism is broken.