First, people think that the bombing was committed because Muslims hate Israel, and therefore they resent any support Israel might get. Second, there is an unholy alliance between the far left and the Islamists, in particular Hamas and Hezbollah, that some of the Marxists consider as liberation organizations. Third, antisemitism is always present and under conditions of crisis, it flares up. To summarize, people hate Jews, and they need no reason to do so.
UN: Gaza could be 'uninhabitable' by 2020 if trends continue (AP)
from the article: Human Rights First: Hate crimes, anti-Semitism on rise in Europe