Authorities often use data to discriminate against dissidents and minorities (e.g. homosexuals). While our current government may be relatively trustworthy, there's no guarantee that that will continue. I'd rather err on the side of caution and control who has access to information about me.
But, this doesn't explain why tech companies should care about my privacy.
In addition to ethical pressure, big tech companies see economic consequences for breeches in trust. For example, Yahoo suffered when it was uncovered that they helped facilitate the arrest of Shi Tao. For big tech to monetize data, they need people to trust them with their personal information. To do that, they need to show a willingness to protect their users.
The question is whether these examples of bad behavior will be public when governments have tools like National Security Letters at their disposal.