If we were never in the EU then all perfect reasonable... However, prior to 2016 the issue was settled, we were in the EU and EU rules applied, folk moved here, with the UKs blessing, to work in industries as diverse as food processing to highly skilled medical research.
To then turn around and take rights away and charge for this, is foolish, the UK is not in a position to lose many key workers, the cream is always the first to leave in any country or organisation,
All that may be true, and I agree it is foolish, but historically, the British have had a very turbulent relationship with the rest of the world.
While some EU citizens clearly viewed themselves as European equally to their own nationality, I would suggest that has never been the culture in Britain, and as a nation we never fully integrated in the way other counties did. The signs were there if you looked for them - we were kind of like the recalcitrant cousin who really didn't want to get fully involved but wanted all the benefits of being a member of the club.
Being a member of the EU was always reversible (in theory). I appreciate it surprised many when it happened, but it was always a possibility, however slim.
In some ways, it seems that those who immigrated here had more faith that we would welcome them than many of our own pro-EU citizens.