"In the modern world, virtually all of our communication involves other companies, and so if those companies can voluntarily act as effectively agents of the government in providing the government data, then the Fourth Amendment is practically void."

I think the point is that the tech companies aren't sharing their users' data with the government voluntarily -- the government is using a combination of questionable, secret court rulings and strong-arm tactics to force them to share. If left to themselves, the companies in question (at least the ones that have spoken out most loudly) wouldn't voluntarily give up as much information as they have been. And not just for idealism's sake -- their own bottom line is likely affected.

EDIT: removed unclear statement meant as a joke.