I'm sorry. I really don't get it. What's so scary about this strip?
It's designed to make the reader "realize" they're getting old.
If "Time" is set so far into the future, why do the protagonists know so little about the world, and why is the technology level of the Beanie People so medieval? What happened in this world's past? For that matter, how come "everyone but us" knew the flood was coming?
Apparently something ended modern high-tech civilization and it never got reestablished (perhaps because all the easily accessible fossil fuels have been used up, and the learning curve from low-tech to high-tech is just too steep without them). As for why everybody else knew the flood was coming, the Beanie People leader said that they tried to warn everybody, but didn't find the protagonists' tribe.
Perhaps the Hill People (who dislike the protagonists' tribe) were found by the Beanie People and told them that nobody lived down by the seashore, thus preventing them from getting the warning.
In this strip, the author accuses Idiocracy fans of being intellectually snooty and self-righteous. How does he reconcile this with his attitude in strips like this and this, in which he declares hard sciences to be necessarily superior subjects of study and anyone who studies soft sciences to be an idiot? I'm not even a big fan of soft sciences, but I think that's a bit much.
I didn't quite read it like that. In the former, I just thought he was pointing out that every scientist has a way of making him or herself feel superior to those in other fields. He does have a point in that mathematics are about as "pure" as you can get, since it has far less in the way of relativity than, say, sociology. In the latter, he's talking to grad students, not actual established experts who would probably seen through the bullshit within one sentence. It's not really so much a comment on their fields as on their proficiency — or presumed proficiency versus the actual lack thereof.
I thought it was that fields like engineering and linguistics have several hard-and-fast rules/laws that really can't be broken (and when the "impostor" breaks them, that's when the "BS Alarm" goes off), but something like literary criticism is extremely open to debate and alternate interpretation. There are no rules or laws to be broken, and even if there were, literary criticism by its very nature is subjective!