According to a Facebook spokesperson, "people trying to block a profile or Page may see an error message if it has been blocked many times within a short period." In other words, the official company line is that Zuckerberg and Chan's profiles may be deluged by Facebook users trying to block them.
That said, when we tried to block a few other pages that seem likely to be experiencing a similar torrent of blocking requests, [spoiler: Trump] we didn't encounter the same problem.
So you can prevent people from blocking you just by being staggeringly unpopular! Sweet!