Sheer size can certainly be scary, but consider that Google and Facebook got where they are by excluding stuff people don't want.

Google has used page rank from the very beginning to show popular pages. Since then, there have been a zillion other teaks to search ranking. (Not to mention that Gmail's spam filtering was an attractive early feature.)

Facebook started out excluding people who didn't go to a particular college, and later, the friend graph helped people avoid communication with strangers.

More recently, Snapchat showed that auto-deletion of photos is something people really like, even if it's technically "impossible" to do perfectly securely.

So it's not just about big companies being in control. Filtering is a really popular feature. Companies that did it well attracted users and became big.