Musar su Salmi 15:3

And his brothers, sisters and other relatives he should love in this manner — that he should assume and have it in mind that they are attempting to bring him to virtues that are dedicated to the service of the Creator, may He be Blessed, and that he should similarly interest himself in them to teach them and correct them and not show them many special privileges or partiality in a matter involving others. For this there is great reward for him, since this fair conduct is a great virtue, as it is written: "And he has not done a shameful thing to favor his relative" (Ps. 15:3).

At that point they had not yet formulated the thought of slandering the land of Israel, they had merely hoped that the conditions would be such that conquest by natural means would not be feasible. Since, as we know, one sin brings other sins in its wake, the spies became trapped by their personal ambitions. This is the reason that the Torah describes their activities as וירגלו, similar to Psalms 15,3: "his tongue was not generally given to evil."