Yeah,,, I think we must understand that 'murder' is 'unlawful killing'. However, in the case of an unjust system like Apartheid, killing for the purpose of a greater good elavates beyond 'murder'. Sometimes unjust laws must be broken.
I believe that the ANC did as much as they could using peaceful 'legal' means,,, but MK was needed to let the people in charge know that you ain't just gonna continue to roll over and take it.
It's a grey area, but that's life.