Or perhaps they are members who are using a public computer in a cafe or a library or borrowing someone's computer and don't want to have their login info recorded on that computer.

I am not sure why one would care if the "lurker" is a registered member or not. Since the site is open to anyone to view and read the posts then I assume that everyone who signs up to post understands that.

And I am not sure why anyone would want a "membership drive". Is there any benefit to the site or to the members to have large numbers registered?

Am I missing something here? I am relatively new with relatively few posts so I am learning as I go.