There's also the (overlapping) question of how much the issue ties into peoples' identity. See "Keep you identity Small" and most of EY's stuff on politics, especially anything that mentions the blues and the greens.
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 ...
If it's worth saying, but not worth its own post, even in Discussion, it goes here.