"I agree with Adobe's philosophy that in general multiply imported versions encourage non-optimum workflows."
That reasoning is all well and good. It is important to establish a best practices workflow .... but if importing duplicates is not in our best interests ... 1. Why did Adobe ever allow users to do this in the first place? Surely the fact this wasn't a recent epiphany.
From my experience, the code to detect duplicates was a bit flaky early on, so being able to override the duplicate detection was a practical necessity. I've not noticed any mistakes in recent times.
2. How does removing the capability really help a new user better understand the import process?
Because in general providing options that encourage poor use of the software by those that don't realise why it's not a good idea does not (IMHO) help a new user better understand the import process.
Another example: if you use "Edit in Photoshop..." with an older version of Photoshop (with an older version of ACR) you get a warning and an option to "render in Lightroom" (and create a copy) or "open anyway". The "open anyway" option is usually not a good idea and creates mysterious errors. I've lost count of the posts on various forums of people who've used that option, and clicked the "don't tell me again" option, and have got themselved thoroughly confused about why Photoshop apparently ignores Lightroom edits.
In general, better not to provide dangerous options, or (if you must) keep them behind warning messages.
3. Why didn't Adobe take the time to inform their traditional users BEFORE they made such changes?
Good question. Tom Hogarty's apology seems to admit they screwed up there. I agree: they did screw up.