I think this is the strongest pragmatic argument. The decision has now been made but I agree with @JTeller3 in principle (I’ve stated so in the beginning of this thread) but that has the assumption that information erasure is not dependent on time after posting – something which @fsflover’s point highlights. Anything other than this is just contributing to a false sense of security.
I’ll add the following from my moderation experience since this change went into effect.
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If users regret their comment, they have a 5 minute grace period to edit it without the revisions being made public. I think these are even only sent to mailinglist subscribers after those 5 minutes in whatever state that is.
My experience is very anecdotal, but I’ve seen this happening (see here) and I think it’s perfectly fine. Email users will see only “deleted” and thus not reply in vain.
@JTeller3, looking forward to reading your dissertation on the subject 
(will do it later)