When Ulysses S Grants father-in-law died a few years before the civil war, he left them his slave. The Grants were dead broke, Ulysses had failed at farming and the slave was worth a lot of money, they could have worked him or sold him to make the their life instantly better. Instead Ulysses took him to the courthouse and made him a free man.
How hard is it to have empathy for others?
It is clear that Jones was previously owned by Dent, but when and how Grant acquired him from his father-in-law, as well as Grant's motivations for freeing him are not known.
See http://www.snopes.com/confederate-history-slave-ownership/ or https://www.researchgate.net/publication/297734845_Ulysses_S... or almost any other reputable source.
It appears that Jones worked on Dent's farm with Grant, so maybe he freed him when the farm failed?
Harder for most people than you seem to think.
That really depends on the person. Some people don't have empathy. As a sufferer of DPDR, a lot of times I don't even feel I have emotion.