"So the UK has now joined the increasingly long list of countries determined to commit political and economic suicide over the issue of immigration."

Not at all! Having a stricter immigration policy should be the aim of every developed country; and for them to require that immigration be based on both legal application and the merit of the applicant. If countries essentially have open borders, in time they will be turned into the same kind of shit-holes as the countries from which many of these immigrants come.

"What led so many right-wingers to reject Reagan and Thatcher in favor of Trump and Boris Johnson?"

They have seen what illegal immigration, immigration based on lotteries, sponsorships, etc. has done to their respective countries, and want to put an end to it. Thank goodness, there are finally leaders willing to stand up for what is right, and protect their own people.