I wonder to what extent this is actually true, and to what extent it's a meme that's grown around (the social network called) Diaspora. I've spent a fair amount of time with people who are part of the Jewish and Zimbabwean diasporas, and I've never picked up on a "dark" vibe to the word. And, as decode points out, the Jewish diaspora refers primarily to the ancient Jewish exile and dispersal from Palestine, not to 20th century history. I see the word more as a part of Jewish culture and tradition that's if anything celebrated, but Jewish readers are welcome to tell me I'm being crass and culturally insensitive.