I'd be hesitant in trusting random anonymous people on the Internet. Mandela was convicted by the Apartheid court of "inciting workers' strikes and leaving the country without permission" and "four counts of sabotage and conspiracy to violently overthrow the government". The Wikipedia article on Mandela says he took part in sabotage and had plans to engage in guerilla warfare against the Apartheid government. I guess that makes him a terrorist by some definitions, but the widely accepted illegitimacy of the Apartheid government and its methods of oppression make a strong case for "freedom fighter" or "militant" being fairer terms to describe Mandela.