Another guidance for the ethical side is the concrete behaviour of working scientists: If they would send you the paper if you asked them by email, this is a clear statement that copyright violation is perfectly okay.
Way back in the day, we would buy reprints from the journal, and then mail them to requesters. And then Xerox machines appeared, and we made our own copies. Now we just email PDFs.
At least in my discipline, authors either retain copyright to their manuscript and can disseminate that freely, or they are able to personally disseminate the final published article (sometimes including on their own website). No copyright transgression occurs in this case.