I appreciate your comments and they are always insightful...
Re: (paraphrased) how is the proposed method ("spam block") any different or better than the current method ("unsubscribe")?
What's proposed, IMHO, is a more graceful way of responding to the spam report than unsubscribing the member (which to many seems rather draconian). Since it would be enabled on a per-group basis, group owner/mods would never see it unless it was enabled.
You mention you direct-add unsubscribed members, but the free plan groups do not have direct-add so it's more problematic for them to get the member resubscribed.