I'd also like to have identification without full registration. I think that should be a core option.
Seems there are three distinct cases:
2. Requiring voluntary identification (typically, name and email address)
3. Requiring registration (verification via email or third-party login).
Wikipedia is a large-scale example of how 1 and 2 can even work together. But, as that site points out, the user IP# is recorded regardless, so there isn't any real anonymity.
Depending on the situation -- the type of site and the site operator -- requiring no ID or voluntary ID means it's easier for the visitor to participate AND it is less invasive, privacy-wise. Imagine being asked for photo ID before able to ask questions in a store, or chat with a stranger in the street. :)