It's not that Israel is somehow 'responsible' for these developments or that its recent actions have unilaterally 'caused' them: after all, there was plenty of Arab antisemitism, Muslim victim-psychology and left-wing anti-Israel feeling around before all of this happened. But there's little doubt that, whatever its moral justification, the military campaign in Gaza has probably made the emergence of a viable two-state solution, with a secure Israel living alongside a peaceable Palestine, less rather than more likely, as well as dampening hopes that the forces of liberal, secular democracy would win out against clerical obscurantism and jihadist militancy in the Arab world (not to mention among the western left).
As other bloggers have documented in detail, many of the protests in the West against Israel's actions have been notably soft on Hamas and have often provided a platform for antisemites and clerical fascists. Anti-Zionist outrage has too often slipped into virulent antisemitism, making it no exaggeration to speak, as Johnny does in this post, of the re-emergence of a kind of left-wing fascism. Along similar lines, see this post over at The New Centrist, which links to an article by Ernest Sternberg on the 'revivified corpse' of left fascism.
The work of anti-totalitarian leftists is certainly going to be harder, but arguably even more urgent, after recent events.