I'm trying to emphasize that you have to look at decisions based on what Custer knew at the time. It doesn't matter whether the Indians were really planning to flee or not; he believed they would, as did everyone else in the army. This was based on prior campaigns and the strength of the three columns in the field. This complete assurance that the Indians would run and that every step must be taken to prevent that was without a doubt a contributing factor to the disaster that ensued. But that was not an attitude created and promulgated by Custer. That was a general belief in the army.
I agree with you here, but what did he know?
a. He did not have any idea of the size of the village other than "it's big";
b. He did not have any idea of the size of the OPFOR at the village;
c. He did not have specifics on the local terrain;
d. He did not have any idea of what actions were happening at the village;
e. He did not have positive confirmation that he had been detected;
f. He did know that the estimated overall strength of the FN was 800-1000 fighters (which as we know now was incorrect, as it only took into account the warriors available on one of the reservations, not on the combined forces. However, Custer could not have known prior to contact with the village at the Little Big Horn that his intel was grossly inaccurate);
g. He did know that if the FN detected his presence that the warriors would engage in a holding action while the rest of the village scattered; and
h. His orders were to locate, and fix the village, and to eliminate the FN as a threat by either getting them to return to reservations, or by military action.
Custer was an aggressive commander of cavalry, with an eye to possible political office, and a somewhat narrisistic personality (wanting the right people to know he had the chops for his duties and not being afraid of self-promotion) that rubbed a lot of people the wrong way. He did not get along with, or have the confidence of his senior subordinates, but did have the confidence of the rank and file.
A slower advance to the village with a scouting and screening force deplowed would have probably allowed Custer to get positive information on points a to e. Custer's mission focus was to locate and fix the village to eliminate the threat, but his aggressive nature and possibly the idea that if it was his force that eliminated the main threat that he could parlay that success into possible political office cannot be discounted as factors that caused him to advance at a pace that generally precluded scouting ahead.
