The Copyright line is not what confers copyright to you – it is the fact that you wrote the thing down. The Copyright line is merely informative. Also, there's no such thing as a common law copyright – copyright in the US is statutory (explicitly within Congress's authority under the US constitution) in all its forms. What registration gives you is certain kinds of extra benefits.

Also, it's not just professors talking about orphan works. It was a major argument in Eric Flint's copyright columns some years ago. Of course, Flint wasn't advocating copyright violation as a remedy.

(Also, there's no stealing involved. But that's a different argument altogether.)