What does the Pasuk mean when it writes "Bocheh l'Mishpechosav"?
Rashi: It means that, when they gathered to complain about the Manna, they did so in family groups in order to publicize their complaints.
Rashi (citing the Sifri): It means that they now began to grumble about the prohibition of incest. 1
See Sifsei Chachamim.
Rashi writes that they cried about Arayos. Why did they cry only now? They should have cried at the time of Matan Torah!
Riva: They did not want to mar the Simchah [of Matan Torah].
Lev Eliyahu (Shemos p.101): Mid'Oraisa they were permitted, for they were like converts. However, in some cases Rabanan now decreed to forbid a convert to his former relatives.
Rashi writes that they cried about Arayos. Surely many had married relatives, like Amram, and now they needed to divorce and break up the family. It is proper to cry over this! Why was Hashem angry? Why does the Sifri call them Resha'im?
Lev Eliyahu (Shemos p.101,2, 105): Everyone is judged according to his ability. They lived through the Makos, Keri'as Yam Suf, Matan Torah, and ate Manna