Let's make a distinction though. Ajax fans may use the Star of David logo (Antwerp in Belgium do the same) but they have very few or none Jewish fans nor any ties to the Jewish communities in their cities. I doubt more than 10% of their fans would know anything about Israeli history or politics or even know where Israel is on the map.
Real Jewish clubs are the likes of Makkabi Berlin, Maccabi Antwerp, Hakoah Wien, ... Clubs formed by Jews and for (mainly) Jews and with close ties to the Jewish communities in their cities. Most big European cities with a Jewish community have such a club, Prague and Amsterdam being notable exceptions which is odd because the Jewish community is or at least has been very big there, but there has not been any specifically Jewish club in those cities as far as I am aware.
In my native Belgium, both Antwerp (which has one of the biggest orthodox jewish communities in Europe) and Brussels have a Maccabi sports club. The one in Antwerp even is very old and has a very long history. The one in Brussels is relatively new and more multicultural, with several muslim players and irreligious players as well, while Maccabi Antwerp has been more distinctively Jewish (although they have also accepted a more limited number of non-jews in the team).
Hakoah Wien has been very iconic and I believe their tour of Israel prior to independence has inspired several Israeli clubs (Hakoah Ramat Gan I believe adopted the name and kits of the Hakoah club in Wien ?)
The idea of some City fans with beer belly's flashing their tool is gross
I hate this sort of chants where football irony begins to border racism. When Israel played in Ireland in 2005 several Irish fans threw bottles at the Israeli fans, shouted stuff such as "where's your foreskin gone" and even some very painful slogans about the holocaust. Disgusting, and many Irish football fans felt deeply ashamed of what their fellow fans did that night. This sort of behaviour IMO should be sanctioned with stadium bans, racism in stadiums is not acceptable.
And PS: it shows some naive generalisations because (while the vast majority of Jews does have the Brit Mitzva) not every Jew is circumcised. Even Theodore Herzl refused the brit on his son, and this is the man who played a capital role in the formation of the Jewish state. So those chants are both racist and showing ignorant generalisations.