You're quite right that freedom of speech and expression is a core American value.
Another core American value is independence of thought and action. We are a nation of grown-ass men and women who do not require a company, a government, or any other arbitrary authority to sign off on the exercise of those rights and liberties which are our common birthright.
So if Facebook chooses not to permit its users to say controversial things, the American response is not to go crying to Daddy to make that mean old mister Zuckerberg be nice, but instead to say: "Well, then, you do just as you please - and be damned to you, because I will go and do as I please." And then, suiting action to word, to set up one's own website, where one may speak as one likes without fear of being suppressed by the ukaze of some billionaire overlord. We do, after all, still have an open Internet. I think it would behoove us to use it.
To that last point, let me reiterate that I have no love for Facebook, and would prefer that such a behemoth, opaque monstrosity - with such an astonishing degree of power to mediate the social interactions of more than a quarter of our entire species - not only did not, but could not, exist. That is far too much power to inhere in any single organization.
Where we differ, I think, is in our evaluation of the most useful method of taking that power away from the organization which holds it now. You seem inclined to prefer that government should do so - an obvious answer, to be sure, but in my view fatally flawed insomuch as that, in taking that power away from Facebook, this government would necessarily gather that same power to itself. (Who else, after all, would you have tell Facebook what to do?)
I would rather see that power, not still further agglomerated into a different monolithic bloc of same, but rather atomized. It seems to me much more in accord with American values that this mass power be broken down and distributed among many individuals, such that each may exercise her rights with the maximum liberty to do so, and none may forbid another from doing likewise.
There are some really exciting projects underway right now to build a framework in which this can happen - indeed, a framework in which nothing else can happen, wherein the construction of a Facebook in anything like its present leviathan form is impossible because it has no apparent benefit to offer. This is a very long-term goal, I freely concede! I may not live to see it bear fruit, if indeed it ever succeeds in so doing. But nothing else of which I'm aware offers a better prospect of upholding those American values which my fellows and I hold so dear.