That turned out to be significantly less dangerous than we anticipated.
...where "we" is limited to people in Western democracies with governments that don't oppress their citizens. People in countries that have less enlightened governments have often had a pretty bad time after posting things online in ways that security services have been able to monitor, track, and use as the basis for imprisonment and worse.
I don't believe that Google is passing data about people to oppressive regimes, but there are damn good reasons why people think privacy is important for all internet users.