As a young man, Mandela was a terrorist, while fighting against an oppressive - some would say "terroristic" - government. He also served time for his crimes, and emerged from prison a different person.
Do you believe that people can never change, and can never outlive past sins? Be very careful when throwing stones like that.
When Mandela died he was not, in fact, a terrorist. He was, in fact, an elder pacifist.
Revisionist history is written by all sides, but the bulk of it seems to come from the political right.