PT18 · S4 · Q5 The ends of modern centuries have been

This definitely doesn't have the same sentiment of [the turn of the century is just any other random day on an arbitrary calendar]. This claim would support a conclusion saying, "It's not surprising that some of these reactions have consistently proven to be wrong." Both sides can't be simultaneously right if it's logically impossible for them to both be correct. But the author's actual conclusion isn't "I can see why they can't both be right", it's "I can see why they are both wrong".

This answer actually makes it possible that both the apocalypse and the utopia people could simultaneously have their reaction to the end of the century validated. It's not giving us a reason why "BOTH groups are likely to be disappointed when the turn of the century doesn't bring about utopia / apocalypse."

It seems like this answer actually does strengthen, but in a different way. This answer is saying, "you guys don't end up getting the utopia / apocalypse that you're expecting, because when you're so convinced it's coming you actually spoil it from happening." The original argument was saying, "you guys don't end up getting the utopia / apocalypse that you're expecting, because the calendar we happen to go off of is totally arbitrary, so the year 1900 or 2000 in some made up numerical count doesn't represent some special moment in history."

Like (D), this does help strengthen, but not in a similar way to the original premise. This answer is saying, "you guys don't end up getting the utopia / apocalypse that you're expecting, because this disappointment happens at the end of every century, but those people don't live long enough to warn the suckers at the end of the next century." And the original premise (and correct answer) are saying, "You don't get the crazy transformation you're expecting because the calendar we use is a totally arbitrary way of keeping track of time, so there's nothing inherently special about the turn of a century".