So here's me (50% southern Greek, 42% Macedonian Greek, 8% Vlach gypsy), with Vanessa (mainly English but with suspicions of Welsh heritage also), managing quite-nicely-than-you next to our Bangladeshi neighbours on one side, Polish one more door down, English-Scottish on the other side. Quite the opposite of what you claim, WAV, we get along very well despite our religious, dietary, or other differences. So much so, that a new song was written precisely to celebrate the fact, called "Street life". The chorus says it all:

"A different story every day of the week
As different as chalk and cheese the faces that you meet
And I don't care much where they come from, who they pray to, what they eat,
But I am lucky living down our street".

Frances Street in Chesham is the practical, real-life, proof to the contrary of your statement, Dave. I have often agreed with other postulations of yours, but not with this one. Not this one, by a long chalk.

Your theory has no legs.