Because people change and we all in the West should have the right to be asshole. When Fascists March against something as laughable as the Jewification of Britain and then ignorantly co-opt something that for many of them would have been abhorrent in the Palestinian flag, then it is good that they get to parade their ignorance. Isreal is a secular state, and there are many Jews in Britain who are right at the forefront in fighting for the rights of Palestinians. Many of the Fascists grandparents fought the German Nazis as British soldiers, so they don't really have a patriotic leg to stand on.