So that said... if someone creates a fanzine by scanning actual public domain comics, and you then scan pages from the fanzine, are you breaking the law?
In theory, no, provided there's nothing involved with the copy that the courts might consider creative work done.
That's why we usually say no thanks. There's no way to know if--for a borderline example--part of a page was drawn carefully for practice and whether a judge would consider that creative (keep in mind that, if I were able to paint and painted an exact replica of the Mona Lisa, I'd have the copyright on my replica, no question).
Professional reprints, for example, almost always recolor and adjust the line art.
There's also neighborliness. We do generally try not to share scans if it's not clear the scanner meant them to be shared. This would be one of the few cases where that would really matter.
