Seriously, though: I actually think there's a case to be made for thinking about whether films, books, etc, created in earlier times are ... what's the word... appropriate? -- for today. Certain comedy shows from the 1960s and '70s, etc, have clearly aged poorly, with the humour no longer so funny to modern eyes. I'd not advocate actual censorship, but it pays to be mindful of the environment in which something was created, and the message it sends out. A good "bad" example is The Birth of a Nation, which is a masterpiece of early cinema, let down only by its bizarre insistence that the KKK was somehow instrumental, in a good way, for the creation of the US.
I don't get why Zulu is a target, though. It always has seemed to me to be rather respectful of the Africans. Individually, they come across as equally brave, their cultural practices are respected, of course it features relatives of the historical Zulus -- and there's even one scene, at the beginning of the film, where one character disrespects the Zulu culture and is rapidly reprimanded (actually two, now that I think of it).
So I don't get the point of the 28 protesters at all. Maybe they haven't seen it.