There are some interesting points in play. For example, how exactly do we take this midrash from Sanhedrin 111a, that it was decreed that Moshe would not enter the land. Rashi cites it on Shemot 6:
|Now you will see, etc.: You have questioned My ways [of running the world, which is] unlike Abraham, to whom I said, “For in Isaac will be called your seed” (Gen. 21:12), and afterwards I said to him, “Bring him up there for a burnt offering” (Gen. 22:2), yet he did not question Me. Therefore, now you will see. What is done to Pharaoh you will see, but not what is done to the kings of the seven nations when I bring them [the children of Israel] into the land [of Israel]. — [from Sanh. 111a]||עתה תראה וגו': הרהרת על מדותי, לא כאברהם שאמרתי לו (בראשית כא יב) כי ביצחק יקרא לך זרע, ואחר כך אמרתי לו (שם כב ב) העלהו לעולה, ולא הרהר אחרי, לפיכך עתה תראה. העשוי לפרעה תראה, ולא העשוי למלכי שבעה אומות, כשאביאם לארץ:|
and the idea of punishment for this early reluctance in his mission fits well with the pesukim and midrash in perek 4 on shelach na beyad tishlach. But what of the pasuk in Chukas of the response to shim'u na hamorim, and the midrash (on Bemidbar 20:12, also brought down in Rashi) that it was only for this and no other sin? I'm inclined to read this as foreshadowing of the future downfall, just as Rashi discusses on Shemot 1:22 the astrological prediction that Moshe's downfall (of not entering the land) would be through water. There might be other ways of resolving this conflict, or apparent conflict. Maybe these are conflicting midrashim, but how does a midrash conflict with a pasuk? But even if such was the gzeirah, was Moshe even told of this at this point? Was it well-known to kelal Yisrael? Why then does Rashi cite the Midrash (on Bemidbar 11:28) that Yehoshua was upset by the prophecy that Moshe would die and that Yehoshua would take them into the land? Though this was still slightly before the spies...
Another interesting point is that we indeed see the idea here of people rebelling while upset about not entering the land. Thus, Datan and Aviram say:
Perhaps we can read this as an emotional reaction of learning they would die in the wilderness instead of settling the land. This would then be an emotional reaction rather than a cold calculation.