agree, but I would suspect that you are legally responsible only if the file is stored on your server. If that was a link to a file stored somewhere else, the people who archived it are responsible. In any case, I understand that as a moderator you do not want ambiguities and prefer to adopt a conservative approach.
My understanding based on conversations that I had a while ago with copyright people at my institution is that, unless otherwise specified, archiving refers to public sharing on any non-commercial website. Rules are usually (probably almost always) different if the article is used for commercial or marketing purposes.