I can kind of understand the argument that there is a history of racism connected with slavery, but the concept of "slave" predates discrimination of coloured people by millenia, closely followed by the word itself, which is actually derived from "Slav" (like you sometimes hear Russians being referred as). But fair enough, seeing a connection to racism is maybe just misinformed.
But "blacklist" (and "whitelist") is just completely absurd. "Blacklist" is a term from a play, referring to a literally black list. Whitelist is just an antonym. Such color metaphors are incredibly common, think wedding dresses or "black death", or black flags, or white lie. Obviously, none of this is connected to skin color. How exactly does your mind have to be wired to come to the opposite conclusion?
As one of the largest (and most criticized) players in political information, one would think that Twitter could maybe do something better about the current situation than engaging in etymological misinformation...