Those companies, being a huge influence on the internet culture and economy, a trend-setter, one might even say the internet gatekeepers - I think they not only should disclose and vehemently oppose any attempts on user rights, but it is their moral obligation to do so.
How is it that individuals and small parties are scrutinized and put down for a single misstep or a character flaw, while enterprises are forgiven, or worse - go unnoticed, for systematic violations of our rights.
Also, keep in mind, that being a big business like Google, inevitably puts you in a close proximity to government and politics. One thing is certain, they do not lobby on our behalf. Though they could. If Google and other giants had a moral compass resembling one of Lavabit or FastMail, perhaps PRISM would fail or never happen.