How exactly does the gemara get to this conclusion? The gemara (A.Z. 5a) puts Moshe’s critique in the context of Hashem having said, “Mi yitein v’haya levavam zeh lahem l’yirah es Hashem…” Bnei Yisrael should have responded “Tein atah!” but they failed to seize the opportunity. Rashi explains that Moshe only criticized Klal Yisrael in our parsha, 40 years after the fact because even Moshe Rabeinu didn’t realize Hashem’s intent and Klal Yisrael’s error until 40 years later.
Tosfos asks: so why was Moshe Rabeinu angry at this point? If even he didn’t realize at the time that Klal Yisrael had done anything wrong, how could he in hindsight criticize them?
Tosfos answers that Moshe Rabeinu had not sinned and was not in need of extra rachamim, so he was not attuned to what was lacking. However, since Klal Yisrael had sinned and did need Hashem's extra help, they should have been sensitive to their own spiritual deficits and responded to the opening Hashem offered. The failure to do so is their burden alone.
My son wanted to bring proof from here to a yesod we once discussed from R’ Shach (I also found it in the Ohr Yahel and see here as well). Chazal say that the Nevi’im and Chachaim did not know the answer to “Al mah avdah ha’arez?” why the churban happened. If the people did not know what was wrong, asked R’ Shach, how could they be held accountable?
R’ Shach answered that even if the Chachamim and Nevi’im could not tell the people what was wrong, each person in his heart knew exactly what his/her own failings were.
Here too, the fact that even Moshe Rabeinu himself did not see the problem until 40 years later is no excuse. Our own moral intuition should impel us even when our leaders do not criticize our actions.