True but it was a political problem for him since he was against slavery. His wife died young and he remarried. What does all this have to do with problems in Chicago as you initially stated?
"One of the worst Democrats was Stephen A. Douglas and yet the left does nothing to dismantle his putrid legacy in Chicago."
First you say that he did not own slaves and then you say that he did own slaves and then you ask why the big memorials to a slaveholder are a problem for the Democrats in Chicago. Did you ever play connect the dots? The greatest Democrat ever to come out of Illinois was a slaveholder and the Democrats are proud of him--you yourself noted all of the wonderful things that he did.