Edit: more info, and some evidence that I was right :) http://usatoday30.usatoday.com/news/world/2008-04-30-watchli...
Not surprising at all.
Dig into the history of the ANC a little. Specifically, look for Umkhonto we Sizwe after the Sharpeville massacre in 1960.
While in no way [edit] trivialising the abhorrent and often vicious apartheid regime of the time, the ANC (and Mandela) haven't exactly been angles, either.
No, to denigrate means to attack the reputation or importance of another, usually in an unfair manner. It's more negative than mere criticism.
On the contrary, one could say they were a bit... acute.
This is not a swipe against Mandela in any way. It's just an example that one man's terrorist is another man's freedom fighter, and how rigid systems can end up giving you politically inconvenient results.
If you make a blanket rule that people with ties to terrorism cannot enter the country, then you can end up "correctly" denying entry to Nobel Peace Prize winners.