Why is an opinion on Gaza more likely to become a part of someone's (from Europe or America) identity than e.g. an opinion on Darfur?
For me it's mostly the network effect. I care more, because people around me care more. I also care more because I have more information, but that again is because people around me care more. If people around me stopped talking about Gaza, it would be just as easy to forget as Darfur.
What keeps this topic alive, is the memetic chain: Gaza is linked to Israel, which is linked to Jews, which is linked to Nazis, which is linked to WW2 and its aftermath, which is linked to our contemporary politics. Also Jews are linked to Old Testament, which is linked to Christianity; in USA, Israel is linked to Religious Right; and the religion is again linked to politics. This all together gives Gaza a high "Page Rank".
Darfur could get some "Page Rank" through the former colonies of European countries, but that link is much weaker and outdated.
The mindkilling emotions are not caused by the human suffering, but by pattern-matching it to the political situation around us. This triggers the feeling of "it could happen to me, too" and switches the brain to the battle mode.
This year the US gave roughly $3 billion to Israel, $500 million to Gaza and the West Bank, and $31 million to Sudan. I care about the conflict between the first two largely because my country funds it so heavily.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.