Japan, notoriously a country with an immigration policy that could in good faith be described as "unchecked".

It’s the rate of increase in immigration, which makes it harder for a country to “take it in and give room for assimilation”. Same problem in Canada, and a good chunk of pathways have been rolled back.

It’s not a simple issue, but very obviously citizens of countries where immigration rate has gone through the roof aren’t happy. Also the usual hatred starts when low income immigrants move into the country, as they’re more likely to work in public-facing jobs (markets, hotels, etc).

You don't have to make every mistake yourself in order to learn from it.

Exactly - they choose not to commit that mistake.