And it was even a failure for the North - sure, in theory they won, and in practice they just let the South stay as they were but poorer and with a few Black people able to leave.
No, it would have led to decades or centuries of resentment between the north and the south and eventually another civil war among those lines. It would have destroyed the union for good. The only purpose of the civil war for the North was to save the union, humiliating the south would have ensured that it would never really happen.
Thaddeus Stevens was proven correct in his opinion that the south should've been treated like a conquered state and the land forcibly given to the freedmen.
The people who want retribution are never the ones to listen after an armistice.