Congress assigned to federal troops a large role in law enforcement in the 11 Confederate states after the Civil War, tasks such as guarding election polling places, arresting members of the Ku Klux Klan
They enforced "hate crimes".
and halting the production of illegal moonshine
And fought a "war on drugs".
and the fomenting of labor strife.
And involved themselves in labor disputes.
Well, aren't those just great! Which such a < cough > restrained role the last time the military had arrest powers, we certainly won't expect them to expand their use this time.
Why do you think these law enforcement activities conducted by the Union Army were bad? If the Yankee Army had stuck around for a few more decades, then perhaps blacks in large areas of the south wouldn't have had to wait until the 1960's to be able to vote. As for the KKK, what do you have against arresting those who terrorized and murdered innocent people?