To Forgive Or Not To Forgive

Moshe Rabbenu is always ready to stand up to bat for Klal Yisroel and defend them no matter how egregious their sins may be be.  However, in Parshas Behaloscha, when they ask for meat at that point Moshe Rabbenu throws in the toil and tells Hashem he can't bear the burden of the people himself.  Why did Moshe find the request of meat to be too much to be forgiven?  Rav Dovid Cohen explains that Moshe Rabbenu was willing to stand up for Klal Yisroel if they were making an ideological error.  Whether, it be not wanting to go into Eretz Yisroel, the sin of the egel, etc. However, a mistake which is sparked by a physical desire he could find no recall for.  Klal Yisroel was expected to be above having such base desires and Moshe Rabbenu saw no redeeming merit for such a sin.  Similarly, says Rav Hirsch, that is why Korach and his entourage had to be wiped out.  The sin of Korach, although he claimed it to be due to righteous reasons, was really a sin due to Korach's desire to be appointed Kohan Gadol.  It was a sin caused by desire which Moshe Rabbenu could not overlook.  A sin of a mistaken thought can be forgiven but a mistake because one is strayed by their desires must be rooted out.