I think it should have been clear I was referring to simple self-crafted statements like "I dedicate this work to the public domain." or people who think it's l

I think it should have been clear I was referring to simple self-crafted statements like "I dedicate this work to the public domain." or people who think it's legal to republish on Tumblr if you don't claim authorship. CC0 is indeed a public domain dedication but there's pages of legalese behind it.