First off, he denied their rights to use people as property, something several other European nations already outlawed. America was severely lagging behind, and it made America look bad to the Europeans, who already hated them. Sure, he made a few unconstitutional decisions, but so did a lot of other presidents. Lincoln made mistakes, sure. But other presidents, like Andrew Johnson, made even worse ones.
Second off, no. He himself grew up with slaves in his family, but once he got older and educated himself in law, and also saw brutal treatment of slaves in person, he knew that something needed to happen. Again, Lincoln probably knew that Europe already outlawed slavery. There was no reason for America to still have them.
Third off, Lincoln expressed many times in many interviews and speeches on his disliking of slavery. He didn't even get rid of the south's rights, either. They felt left out because Lincoln got office, and felt left out. The reason for that is, even though the South didn't even have Lincoln on the ballet, they had two Democratic candidates, and the south was split between them. As such, the more populated northern states voted Lincoln, and he won office. In reality, if there was only one Democratic nominee, perhaps he could have won.
As such, the south wasn't happy, even though it was their fault that they decided to have two democratic nominees. They succeeded from the union as they felt left out of the elections. As such, South Carolina attacked a Union fort, and started the civil war.
Yes, I know slavery was a huge part of economy in the south. But eventually they would become increasingly poor, due to not being as industrious as the north, who had more workers and thus more money. Not to mention even when the south finally came back into the USA, they still didn't follow the 13th amendment. They still made laws to make sure black people couldn't do a lot of things white people could. So even after loosing the war they still continued their racism.
The problem of segregation isn't entirely fixed even to this day. We have a lot less segregation, sure, but there are still racist people out there. My grandmother was threatened by the KKK because she married a black man. Many of Lincoln's works were never completed because of his assassination and the south's defiance to the 13th amendment. The south, in itself, has done a lot worse than Lincoln ever did. (Just look at the 1960s)