BecomeMe

You can take something from the public domain and sell it. There's plenty of public domain books sold. It just means that everyone can access it and use it equally. You can record everything you overhear at the store and use it for writing a story or whatever.

Although what you say sounds true. These comments are written and signed, easily attributed to the owner. Every document like that in the past has been the property of the writer. Same thing with images. I don't know how Reddit can claim any comments are legally theirs without "consideration" as you say.