Following Bnei Yisrael’s complaint about the man, the Torah tells us that, “V’ha’man k’zra gad hu, v’eino k’ein ha’bedolach.” (12:7) Rashi explains that the Torah is telling us how wonderful the man was, showing us just how silly and baseless the complaint of Bnei Yisrael was. In a similar vein the next pasuk tells us that the man could taste like whatever food a person desired. It was an incredible food – the people should have been gobbling it up. The Torah then adds an additional detail. “U’b’redes ha’tal al ha’machaneh layla yeired ha’man alav.” (12:9) The dew would fall at night, and next morning, on top of the dew, there was the man. Unlike the previous pesukim, this pasuk doesn’t seem to be telling us anything incredible about the taste or quality of the man. The dew fell and then man fell – so what? Why mention it here?
Moving on, the Torah tells us that Moshe heard the people crying, each by their own tent, and Hashem was angry, “u’b’eini Moshe ra,” it was bad in Moshe’s eyes. It sounds like until now everything was A-ok, but now Moshe got upset. Why didn’t he get upset right away, when the people started making their baseless complaints? What set him off only now?
Finally, we have Moshe’s incredible speech in which he asks Hashem how he is supposed to handle the burden of such rebellious people. This is the first time Moshe has had such a reaction. If Moshe was able to handle the cheit ha’eigel, why couldn’t he handle this challenge? (R’ Soloveitchik has a great shiur that addresses this question that you can find quoted many places.)
Chasam Sofer explains that it was probably only a people at first who started complaining -- rebellions start with a few vocal people, not a mass uprising. The rest of Bnei Yisrael stood on the sidelines, watching, waiting. What would the reaction to these rabble rousers be? What punishment would they invite? The people woke up the next morning, and incredibly, “u’b’redes ha’tal al ha’machaneh layla yeired ha’man alav,” the dew had fallen, the man had fallen on top of it, and nothing had changed from the day before. The miracle of the man did not cease, the food was not cut off, and life seemed to be the same as always! At that point, things began to snowball. Since there were no consequences, the rebellion expanded. There were now more people involved, “ha’am bocheh l’mishpichosav,” and Hashem was angry at the people as a whole.
What upset Moshe, “b’eini Moshe ra,” was not the rebellion per se – this wasn’t worse than cheit ha’eigel. What bothered Moshe was the fact that Hashem had done nothing to halt events before they snowballed. What bothered Moshe was, “u’b’redes ha’tal al ha’machaneh layla yeired ha’man alav,” the fact that the man had fallen as it always had. Moshe understood that as the leader of Klal Yisrael, it was his job was to give tochacha, to deal with complaints, outbursts, problems, and guide the people to do good. But he also assumed that it was not his job alone, it was not “masa ha’am ha’zeh alai,” just his burden. He expected Hashem to also play a role in curbing the people's bad behaviors.
A tactic all little kids try is when parent #1, father or mother, decides to punish them in some way, they go to parent #2 and try to get their way. If the parents are not on the same page, it makes for problems. Moshe was in effect telling Hashem that if he has to sometimes take a tough line and give tochacha to Klal Yisrael, Hashem can't still be dispensing goodies to them as if nothing was awry.
But as the Chasam Sofer says succinctly, “Ze’hu darkei Elokeinu yisbarach.” Maybe there would be fewer people who went off the derech if the millionaire who was mechalel Shabbos lost his fortune, or if a lighting bolt immediately struck down wrongdoers. I imagine more people would listen to the Rabbi's speech Shabbos morning if they knew that if they stepped out of line, there would be real consequences. But that’s not how it works. Hashem gives us a long rope. The Rabbi still has to give his speech and try to get us to do good, and hopefully he succeeds, but even if he fails, Hashem does not take away our lifeline.
See Sefas Emes 5644 who interprets the whole parsha here to the credit of Klal Yisrael. The people had a ta'avah, and they started crying, saying that they remembered the food they ate for free in Egypt. What they were crying about is not the fact that they didn't have food. What they were crying about is the fact that they felt such a ta'avah! They were crying that they had hirhurim about the past in Egypt. Amazing.