Nelson Mandela, saint? No. He was a man, who made some mistakes, perhaps his biggest one was in leaving the ANC to unspeakably awful men and in not purging the party of its Leninist culture.
The AIDS-denying, Mugabe appeasing Thabo Mbeki, who, had he been a white Afrikaner, would be blamed for genocide. The rape-denying Jacob Zuma, in a country where 1 in 4 men admit to rape. I see few feminists bemoaning the abject failure of the "new" South Africa to confront this culture.
However, I resist the claims of some that he should be dismissed as a terrorist and a communist. That blanks out the reality of South Africa's white-supremacist regime. It was sympathetic towards Nazi Germany during the war, and had distinct parallels in applying a non-eliminationist view of racial supremacy. Apartheid itself was strongly supported by white far-left trade unions, who didn't want black workers taking their jobs. A argument, which at its fundamental roots, is still used by protectionists without the overt racist component.
Mandela lived under a regime that not only denied him and other black people in the country basic standards of citizenship, but didn't tolerate dissent unless it came from white people. Even then, the regime would use accusations of communism to attack many criticising apartheid. It was the proud Helen Suzman who maintained the small opposition in South Africa's Parliament, as the apartheid regime increasing became fearful of invasion from the post-colonial regimes to its north and of revolution within.
South Africa was a brutal authoritarian state that brutalised the vast majority, and explicitly legally denied them opportunities in business, education, science and culture. In that environment, it is hardly surprising that the ANC - in resisting this - would turn to violence, after the awful Sharpeville massacre.
The state did violence to the black population, it did not allow free speech, it did not give it options for political expression. The black population faced authoritarian rule that they had no say over, they were non-citizens, with the police and the courts almost entirely beholden to those who ruled them.
So given the choice between Gandhi-esque non-violent resistance, and having protests of unarmed school children gunned down, and taking up violence yourself, it's hardly a surprise the latter was taken up.