>But the committee a hostile environment for the people bought before it; if the politicians just wanted information they'd do it in writing or chat to Zuckerberg at a party or something.
Generally speaking, committee's don't happen if there is no reason to believe that any of the alternate means you brought up as examples would be sufficient to resolve the problem. In fact, many of those may have already been addressed or attempted to unsatisfactory result. The legislature has organized and tasked the committee with this investigation as an expression of the "Will of the People" to get to the bottom of business of redressing the grievances of the Constituency, and building policy on the basis of the facts collected. In Facebook's case, largely prompted by not adhering to a previously unnecessary to enumerate social norm, which many people have begun to become concerned with Facebook's primary business model being reliant, and the consequent leveraging of advantaged position via network effect exploitation to prevent competition.
As a corporate citizen of the United States, there is no adversity here. You're in this country, granted legitimacy by the authority of our institutions. If the political apparatus taps you on the shoulder and deems it necessary to look into the facts of what you're doing, nothing at all should change about what you're doing or the answers you give. That behavior of manipulating the response you give in response to interrogation by Congress is analogous to anti-debugger code; obfuscation being an act of perjury. This is fact finding and policy building by duly elected representatives. There should be no adversity. No legitimacy or illusion of legitimate competition acknowledged.
This is humanscale debugging by an authority mechanism implemented by a distributed decision making and consensus engine in the form of a Congress of elected representatives. I don't know about anyone else, but I don't accept the right of a Corporation or an Executive to evade or deceive official legislative apparata. The called already has going in their favor that a great deal of the population are highly resistant to meaningless change, and that there needs to be a non-trivial consensus for change.
Now I fully acknowledge we may have gotten away from the ideal of how things should work, and that when you're dealing with human beings, the level of nuance and communications overloading associated with a state bearing comment skyrockets; but that still does not to me justify lying by omission or outright to your legislature or it's representatives, or intentionally wasting their time for your gain or to intentionally frustrate policy making. If you can't be honest to the collective proxy of $the_rest_of_the_nation, you've got your priorities all sorts of misaligned, and if you're feeling that threatened by the experience, maybe, just maybe, it's finally coming back in unequivocal terms that something needs to fundamentally change about your operational model. I also acknowledge that making the determination of what is "frustrating policy making" and what is just best effort is left fuzzy, and in that fuzziness creates a dangerous policy tool to be abused. I make no claims or suggestion to what should or shouldn't be done in the event thereof, or what the determination that obstruction of policy making has occurred looks like. I'm only pointing out that if you accept as legitimate "defensive legislative perception management" you've undermined the status of the legislature from "wielders of the power of the collective social apparatus, and the authority and access to privileged information that comes with it" to "For sale: invest in a full time employee to haunt enough representatives, and you too can have a law."
There is no illegitimacy in any question being asked. Axiomatically, this is basically people with as close to societal root access as you can get trying to build a realistic representation of the socio-governmental system in order to plot a reasonable course to satisfy $rest_of_the_country.
TL;DR: So long as everything is being done by the book; there should be no self-preservation or overt attempts at manipulation being acceptable. Only as accurate of a rendering of facts as possible, and where a subjective question is asked, a candid answer provided.
For it to be any other way reeks to me of dysfunction, and an overt admission of a lack of integrity, and standing in opposition to the very thing that grants you the legitimacy and capability to live in the manner you desire.
From a social and civic point of view, it isn't and shouldn't be a contest. Just a mechanism at work.