"how common inter marriage was, for that is the only way proper integration can be achieved ......and it must be achieved or society will not survive."

That's complete nonsense. All over the world different communities live alongside one another, geographically or socially, with a little or a lot of blurring and the edges when personal relationships come into play.

Look at group of schoolkids from the cities out in the country for a school trip, DOE or whatever. Or just comming out of the school gates on a normally day. Faces of all colours in mixed grouped chatting together as they go along. Or many workplaces.

You are making stuff up.