Ezekiel Starkweather:
"Well...Yellow hair could have a...accident. Been known to happen-even for famous generals recorded throughout history. Hmmmm?" He raised an eyebrow, preparing himself how Custer was so essential to the timeline he could not be harmed.
More like the fact that if Custer
dies, someone will spin it as assassination even if it's subtle, and then
a) the U.S. Army
officially sweeps in to murder the Lakota, and
b) you have several hundred hungry mercenaries left to live on the land with no overall commander. That is, you just made several hundred bandits.
Aside from just killing random natives (probably with some rape and torture thrown in, because these men are bored and came here to kill certain folks) and decimating their food supply, said bandits will provide an excellent recruiting tool for the Ravenites.
You need to
capture Custer. And get bread and eggs.