Because the NSA keeps tabs on the entire world, they are able to find the source of terrorism. They share this information with the 'five eyes' and in a way keep much of the world safe.
That's the justification they use for mass surveillance, but it just isn't true. Terrorists aren't communicating via Facebook or GoogleMail. They are using encrypted lines of communication.
Because companies know so much about us, they know what kind of technology we use, what kind of technology we will buy. This is not only good for the economy, but also technological advancement of the whole world.
This can be known from sale figures, it doesn't require mass surveillance.
Because companies sell our data, we are able to use their services for free. How would you feel if you needed to pay a subscription for google maps, facebook, twitter, email, or pretty much any free service that you use?
I don't use Facebook, Twitter, or any other social media. I use encrypted email providers which are free. I don't use Google Maps, but use a free alternative which doesn't track me. There are free and privacy conscious alternatives for pretty much everything. Even Tor is free to use.
There is good and bad to the invasion of privacy. Where to draw the line?
There is no good invasion of privacy.