Easy! anything that gathers as much personal info as those sites could use it for ill at any time in a number of ways.
Google want to make it possible for you to search for things like your family members and for google to be able to pin point them life.
It also wants to be able to answer questions like 'What should I do today?' accurately for the person.
This kind of data collection is a gate way to total lack of freedom, because it could become that if you are not with them then you are an outcast and society no longer recognises your input.
Knowledge is power and these sites and stores of knowledge and data.
We've just gotta hope for enlightened people in charge :/