Anonymous users need to provide at least minimal identification.

I'm not happy when I get a new fan, and go to look at their profile, only to find "you don't have permission to view [this person's] profile." If they are following me, and gain access to my profile as soon as they choose to fan me, then I should have at least basic access back to theirs to find out where they are located, or what their real name is. When I visit their profile, I don't even get a block button!

(I do know I can block them by choosing the pull down in the original Alert box.)

Plurk wouldn't work as well if everyone set their timelines to private. And while I understand some people think they have more to hide than others, private users should then by default be blocked until they are given permission to view, not letting it be a passive action.

"Because your timeline is set to private, this user must approve you as a fan. Please provide a personal note to the person you wish to follow."