It not just the Syrian crisis they have bad experience with. Many European countries let lots of poor Muslims from North Africa and Turkey in as labor migrants between the 50’s and the 80’s. And many of those European countries are now dealing with the negative consequences from the descendants of those migrants. Among those migrant communities there is, even after a few generations, still high unemployment rates, high dropout rates and high crime rates (and some of those criminals later formed terrorist cells in Europe). Even compared to other migrant communities the numbers are bad. And the main cause of that is that their grandparents who came here didn’t integrate properly into society and didn’t raise their kids well and of course instilled conservative Islamic ideas in their kids’ head (antisemitism, homophobia etc) so those kids also aren’t integrated when they turned into adults. And that’s because most of those Muslim labor migrants were illiterate subsistence farmers with no education and religiously conservative. People in Europe are rightfully afraid that the same shit will happen again when lots of low educated people from the Middle East will come to Europe.