Interesting context of this 34% number:
...he describes as “alarming” the finding that only 34% of Muslims would report someone to the police who was involved with people who support terrorism in Syria. But for the survey’s “control” group – consisting of randomly selected people from across the country of all or no faiths – the figure is only 30%. And other polls have found that 94% of British Muslims would report someone they knew who was planning an act of violence to the police.
Source: http://www.theguardian.com/commentisfree/2016/apr/12/what-do-muslims-think-skewed-poll-wont-tell-us
As to how worried we should be about the results of the poll: these are just people's opinions. Having opinions, even ones that we consider vile, is not against the law nor is it worth getting bothered about, unless and until they translate into political power.
There are no Islamic political parties in Europe. The small number of Muslims who are politically active are members of the existing mainstream parties and support their programs. The rapid rise of the far-right populist parties across the continent and the associated threat to our civil liberties is a far bigger worry than the private opinions of the Muslim minority. Imagine a world where the National Front gains real power in France, or UKIP in Great Britain. We would be right back in the 1930's. Such parties now have popular support in the region of 20 - 30%!
Call me when there are established Muslim parties in Europe that gain more than a few percent of the popular vote in elections. We really should carefully separate facts from hysteria.