How do we understand what the sin of the Meraglim (spies) was? 

There was nothing they said which was technically incorrect – so why were they punished for what they said?

Iit is similarly difficult to understand what the Jews did wrong by listening to them – after all, there were 10 who gave one sort of “intelligence” report and only two who gave over one of a different kind? Can we really fault them for not taking the majority report – and especially to blame them to the extent which G-d does, with such a drastic punishment?
Rabbi Yitzchok Arama (1420 – 1494) in Akeidas Yitzchok explains that the core of the sin of the Meraglim was that they presented their view of what the Jews should do concerning entering Canaan. That, he says, was never their role. They were sent on a fact-finding mission, and they should have come back and presented their findings to Moshe, Aharon, and the Elders, who would make all the final decisions of what to do.
Because they presented their findings as a judgment call about what to do (first by saying, (13:28) after describing the actual land “אפס כי עז העם הישב בארץ” –  “However, the people who inhabit the land are mighty,” and then when they contradicted Calev and Moshe by saying (13:31) “לא נוכל לעלות אל העם כי חזק הוא ממנו- We are unable to go up against the people, for they are stronger than we are.”
In doing so, they overstepped their boundaries (as the Midrash explains, because of their self-interest), and they were punished for what they did. Man must always remember what his proper role is in everything, and not assume authority he is not fit for.
It is for this very same reason that the rest of the Jews were denied the ability to enter Canaan – to be the generation that would establish Eretz Yisrael. They should have recognized that the proper role of the Meraglim was not to make this determination but to relate their findings to the leadership. At that point, it is the responsibility of the people to recognize that they should be following their leaders, not those who are, in essence, rabble-rousers.


 

How do we know that they are merely trying to raise a fuss instead of completing their mission? We know that from where they go when it is time to submit their report. They did not go to Moshe and Aharon and the Elders – because the agenda of the Meraglim would have been thwarted by that – they would have used their information and come to a different conclusion. Instead, they decided on “transparency” and took their case “directly to the people” where they “blew the whistle” on the impending invasion. That itself should have been its own red flag.