I don't think that's the case. Is it moral to exploit human psychology when developing addictive features that pull people into the site over and over? Is it moral to sell user information to advertisers so they can emotionally manipulate you into buying crap you don't need? Is it moral to design interactions that evoke outrage and disagreement in order to increase engagement? Is it moral to track user activity across the web, outside the company's site?
I don't think any of these things are moral. These practices might not be necessary for a site like FB (then again they might), but this is the model they all seem to choose. And that's what actually matters.