Interesting reaction to the phrasing here. I read OP as framing Lincoln through the eyes of the people who suffered the consequences of his decisions. History is messy. Even unambiguous positives like ending slavery come with a ton of collateral damage. If that collateral damage is your husband or brother coming home in a pine box, you're likely to have a poor view of those who caused it.
A few questions to consider:
1) If Texas or California were to secede in 2023, should the rest of the United States declare war on them and force them to return to the union? What if that war costs the lives of 500k people? 1 million? How many deaths is too many deaths to maintain the geo-political status quo?
2) There are places in the world today where slavery or near-slavery like conditions are a fact of life. Does the United States have a moral obligation to intervene? US interventionism in recent decades has led to unaccountable suffering for the people of Afghanistan and Iraq. The American South suffered a similar fate during and after the civil war.
All that to say, big evils like slavery or Nazism tend to distort historical objectivity. Any cost seems small, any act defensible, as long at it helps end the big evil. Once a historical figure becomes canonized, the negative consequences of their actions get glossed over.