Received from Shal Farley at 9/27/2018 11:55 PM UTC:
J,I was thinking more along the lines that there might be some flaw in the idea.I don't see any flaw, exactly, but the limitation of not receiving message content by email would be a bit of a show-stopper for me.
I think calling for a "via web only" group begs the question when what is really desired is a group in which all members remain anonymous.
It strikes me that all it takes to implement a group in which no email addresses are ever exposed is for all mail posted to such a group - via the web or via email - to be posted by Groups.io with a bogus "From:" address and with any other potentially identifying headers stripped. The address of the group itself makes the most sense for a "From:" address because then a reply either via the web or via email would go back to the group.
It also strikes me that such a group will lose any significant sense of community unless some sort of "Display Name" that would have no connection to the real life identity were required, but I won't ever be joining such a group so don't really care. Just saying.
Also... Owners/Moderators would need to be able to identify problem members in order to deal with them. The activity archives probably could be used to provide this info if information sufficient to tie a message to a member account were retained there.