I remember having discussions with some friends and classmates about the plague of darkness. Rashi (in next week's parsha) brings up the famous Mechilta that only one in five Jews survived the plague - the rest of the Jews, being deemed unworthy of redemption, perished and were buried. The reason that this was done during the plague of darkness was so that the Egyptians should not see the Jews dying in the plague.
Of course, the Mechilta goes on from there to describe that some state that it wasn't one in five that survived the plague, but perhaps one in fifty, or even one in five hundred, or possibly even more (as sworn to by R. Nehorai)!
I really don't want to delve into the issue of Jewish population growth in Egypt and how growing from 70 people to a few million in the span of only a bit over two centuries is nothing short of miraculous (which, I guess, it was). But to say that there were over a billion Jews in Jews during the plague of locusts (2 million Jews [a conservative estimate] * 500 = one billion!) is simply just too far fetched to believe.
In any event, what I really wanted to focus on was the plague itself and its effects on the Jews and the Egyptian reaction (or lack thereof) to it.
When discussing this with other people who take the midrash at face value, the first thing that I usually bring up is the fact that if 80% (at a conservative estimate!) of the Jews in Egypt suddenly disappeared, I find it very hard to believe that the Egyptians would not notice that they were missing. I know that if I woke up tomorrow morning and found that 80% of New York's population suddenly vanished, I'd notice very quickly, even though there would still be over a million and a half people in the city.
The standard reply I get to that is that the Egyptians were too busy reeling from the effects of the plague to notice the sudden drop in population. My answer to that, is that no matter what I was going through personally in my life, if four out of every five New Yorkers suddenly vanished (and certainly if more did so), I'd notice it once I spent more than ten minutes out of my house. I find it highly unlikely that the Egyptians would fail to notice that so many people suddenly dropped off the face of the earth.
The next objection that I bring up really doesn't apply as much to the one in five theory, but far more so to the one in fifty (or more) count. Specifically, the Mechilta tells us that not only did they die, but that they actually buried their dead. The plague itself lasted no more than seven days, and yet I find it hard to believe that you can bury close to a billion bodies in the span of seven days. Even if you rely on the one in five number, you are left with the question of where all these bodies are buried -- eight million graves must take up a lot of room, even using mass graves. And if there were a thousands of freshly dug mass graves (or eight million individual ones!), I again find it hard to believe that the Egyptians would not notice.
In short, I always failed to understand how the Mechilta made the case that the reason the Jews had to die during the plague of darkness was so that the Egyptians would not notice that the Jews died in the plague (and in a plague when no Egyptians died!).
Rabbi Uri Cohen, of the Center for Jewish Life in Princton, in discussing the number of Jews that died during the plague, quotes R. Shimon Schwab. (PDF) R. Schwab maintains that the numbers are not entirely literal. Just as it is possible to interpret the verse "Kol D'mai Achicha" (your brother's bloods) in the story of Cain and Abel as referring to Abel's future descendants who would never be born because of Cain, so to the numbers here don't refer to the actual number of Jews who might have left Egypt if they'd lived, but to their descendants.
I find that explanation troubling, for one simple reason. If the Torah (or the Mechilta) would have given a raw number (eight million Jews didn't leave Egypt) or just a vague statement (such as "Kol D'mai Achicah") , then I might be able to accept that explanation. But since the Mechilta gave the number of Jews who didn't leave as a percentage, I find it difficult to accept that this can refer to future generations. Unless R. Schwab is telling us that the small number of people who died in the plague of darkness (because he doesn't hold that the actual number of deaths was so high) were destined to have so many and far more children that they would be the ancestors of 80% (or more) of the Jewish nation in the future, his statement simply cannot apply.
Of course, if one simply translates the verse "Chamushim" as "armed," all of these problems go away. :)