I am not sure that Grant was a "bad" person. According to plenty of sources he did like to drink. This makes nobody a bad person.
He won the Civil War and will always be remembered as a great general.
The problem with Grant was that he was horribly ineffective as president including the fact the country faced its largest recession under him. In his cabinet he surrounded himself with friends, instead of the best people. He broke up the Republican party, further messed up Reconstruction, and (even though he did not intended to) messed up the situation out West with the Native tribes, and there was a nasty escalation in hostilities, including the Black Hills War.
He was a horribly ineffective president, and the
historical rankings of presidents reflect that.
Great general, horrible president. That's the memory of Grant. Same man. Cannot divorce the general from the president.