One man's terrorist, is another man's freedom fighter.
Whilst I don't condone violence, I can see both side of this argument. your complaint is that Mandella used bombing as a weapon. The US uses bombing as a weapon. They both kill. One is an organisation struggling to free an oppressed people. One is a rogue nation trying to secure resources.

If you are on the receiving end of either bombing, you would be terrorized, and they perpetrators would be terrorists.

For those doing the bombing, they feel it is a legitimize action to achieve their desired goals.