I mean, I think the Radical Republicans let the South off fairly easy, given the treasonous aspects of the insurrection.
Letting whites continue to treat African-Americans as chattels (Jim Crow, the indentured servitued of sharecropping) and throw in a century or more of abject denial of suffrage. And the continued looking the other way at violence, lynchings, denial of basic human and civil rights and what-not.
What was on the table in 1865 was that the south accept these positions: states cannot leave the Union. Slavery is done, not to come back. What Grant and Sherman told Lee and Johnston was, accept these conditions, stop fighting and go home.
The southern states repealed their secession ordnances, and ratified the XIII Amendment (the amendment would have have gotten the required 3/4 of the states without ex-Confederate states' ratifications), then held elections in the fall of 1865 and sent their delegations to the session of Congress scheduled to start in December 1865.
That was when the Republicans realized that the southern states had elected congressional delegations that did not include many Republicans. Having won the war to force the southern states to remain in the Union, it dawned on Republicans that southern states did not like Republicans very much and would not elect them to Congress. The GOP would become the minority party when it included delegations from the southern states, so Republicans refused to seat any of the southern congressional delegations (despite the Constitution's Art. V provision that "no State, without its Consent, shall be deprived of its equal Suffrage in the Senate").
Then the Republicans realized they had to disfranchise southerners or they would have to repeat the process. They needed to manufacture Republican voters to replace them. There were not enough carpetbaggers to do the trick. Then the GOP found what they needed: black voters. In 1865, black men voted in
no state south and west of New York. In Illinois, it was illegal to
be black. Before 1865, Republicans in northern states had absolutely no interest in black voting. Now, when the GOP needed voters, they wanted freedmen (mostly illiterate and easily manipulated) to vote. So most of the whites were disfranchised and freedmen were enfranchised to get the political result Republicans wanted.
William T. Sherman in 1865 wrote: “The whole idea of giving the vote to the negroes was to create just that many votes to be used by others for political uses.” (O.R. XLVII Pt 3, p. 586)
Senator James Dixon of Connecticut said that “the purpose of the Radicals was the saving of the
Republican party, rather than the saving of the Union.”
So Republicans sowed the wind ...
with a line of gasoline poured in their path…
