In my experience, the people who find these things the most offensive are the people the barb is pointed at. Privileged white people--who have nothing better to do than run around worrying about what other people are thinking out loud, trying hard to make sure that the whole world is protected from harmful speech, but who do nothing about actually solving things like the AIDs problem in Africa--are exactly the target of these kinds of comments.
These comments call out and critique the people who only care about Africans when someone says something that can possibly be interpreted to be offensive to them. Of course, privileged white people then use the alleged racism as a shield to hide their own hypocrisy behind and make blanket statements to the effect that there is some universal, writ-in-stone definition of what's offensive.
Now that the mob has doled out justice and protected all the Africans from a menace like Saccio, they go back to Whole Foods after their yoga classes and continue right on not giving a damn about how shitty things are in Africa.
If you find that tweet offensive, perhaps you should pause for a moment and consider that maybe, just maybe, it feels that way to you because you were the intended target.