When I was at comprehensive school I was in the mix with all sorts of people, from all sorts of backgrounds, heading for all sorts of destinies (although obviously this being an oxfordshire comprehensive it was basically totally made of up of white people).
Then I went to University and already there was less of a mix. And I gravitated towards the people who liked the same music/culture etc. — who were, in an institution where being left wing was already presumably the prevailing normal, more left wing than most.
After Uni I worked quite a few low-paid jobs in warehouses and offices, and was once again in the mix with a wider range of people. And that's when you start hearing stuff like anti-immigrant opinions cropping up again. (You'd only hear these in University world swathed in irony.)
Then I somehow started zeroing in on a 'proper' career (God help me) and the mix steadily disappeared again — where i work now is somewhat mixed in terms of nationalities, sexuality, race — but it's all middle-class, university educated people who by consensus believe that brexit is terrible, trump is satan, etc.
I don't disagree with these opinions (obviously) but I do find it interesting how you can grow up in a quite mixed environment and then by dint of education/profession end up not knowing anybody who thinks anything different from you.