People shouldn't be asking that; they're installing a launcher. Do people ask that when they install LauncherPro? I thought people generally understood that Facebook Home adds new Android-level UI features rather than just being a normal app that is launched from the app drawer?
The ones that do understand that launcher and lockscreen are different.
Facebook Home replaces both, and remove some major aspects of the Android UI that most launcher/lockscreen replacements DON'T change: things like getting rid of the notifications bar, changing the lock screen slider, changing the way that you get to apps
It's a very different imagination of how to use your phone. I'm not at all surprised that many people don't understand it and/or don't like it.
Given that you have installed it you then saw how much it differs from the traditional android idea of a 'launcher'. It genuinely is hiding it all away. You can see the pathway that Facebook wants to push the users, essentially fully hiding the idea of having on phone contacts and messaging. That's why it's not really a launcher so much as Facebook allowing you access to your phone (IMHO).