Only if you don't think about it.

First you should stop and think: What is a customer?

A customer is someone that a company makes money from.

Then you think: What money have I given Facebook?

None (or extremely little)

Then you think: But Facebook makes billions. How do they do this?

They have loads of very targeted adverts.

So we who are Facebook's customers?

Advertising companies.

What makes ad space on Facebook valuable?

Their ability to target those ads to the right people based off of the data they have about them and to get you (the product) to see those ads.