Why? Is it because you have a view of history which has been whitewashed by revisionists who have been eager to bestow sainthood upon Mandela? Yes, it is true that after 27 years in prison, he emerged a changed man - he forgave his captors, and spread messages of peace. He preached, but more importantly, he practised reconciliation. He
was an inspiration.
However, don't forget that in 1961 he broke with the ANC which were then moving towards non-violence, and created a terrorist wing called Umkhonto ke Siswe. For this he was jailed, but continued to sanction acts of terror against civilians including the
Church Street bombing in 1983. Whilst he was behind bars, his wife Winnie continued acts of terror against both the white and black population, including the practise of necklacing where burning car tires are placed around victims necks, and cutting off noses of blacks suspected of treason.
He supported Arafat (back then, a trenchant terrorist and prior to his change of heart which saw him win the Nobel peace prize). He and Gaddafi were close - accepting donations from the Libyan leader at the same time Gaddafi downed Pan Am flight 103.
I am not saying that Mandela wasn't a great man, but he needs to be viewed in proper historical context. Nobody is (or was) truly great - Gandhi had some strange ideas about health (including sleeping with many naked young women), Mother Teresa with-held palliative care in the misguided belief that pain and suffering brought people closer to God, Pope John Paul II forbade the use of condoms thus helping spread HIV in Africa ... and the list goes on.