So, you're saying that terrorism...is...legitimate?
Don't be silly. He killed noncombatants, more or less at random, to further a social/political viewpoint. That's terrorism.
No, I am saying that allowing Roof to claim he killed those folks for a reason is to allow him some form of legitimacy, given that one mans freedom fighter etc etc. Like it or not, throwing the term "terrorist" around for this kind of thing does make people think of PIRA, of the Irgun, of the Red Army Brigades, of Baader-Meinhof and the rest. He isnt one of those.
Roof is a murdering scumbag who shot nine innocents in a church. He really doesnt need any other label.