This is a human trait, people do not see the wrong on the things you benefit from.
For example, did you ate beef or fish lately? When was the last time you thought about the animals that were killed in order for you to eat them. Have you seen the sacrifice of an animal needed for eating it. In Mongolia or Middle East nomads will sacrifice the animal in front of you before eating so you know what you eat is the best they have.
Imagine that cows were able to think like humans, and remember what you did to their veal. As a children I worked feeding cows and they are not as stupid as people believe, and they like horses have emotions and personalities like humans have.
When humans personally benefit from something it is very easy to just rationalize it. Humans rationalize everything.
Workers on facebook are multimillionaires that are pretty happy about their life becoming the new central intelligence of the World. They will rationalize it as a good thing focusing on this service being needed and useful for the world, as it is.
The problem is that even when the best of intentions, Governments, and secret services of countries want to use this service for nefarious purposes in the same way that if you centralize money in one place, some people want to take it by force if necessary, if you place too much personal information in some place, some people will want to take it for their own use.