Europe has many illegal immigrants.
Many people in the EU don't want to be ruled by an unelected and unaccountable supranational organisation either, but that is just what is happening. Once you have a supposedly benign but unelected and therefore un-removeable ruler, what happens when someone malign chooses to manipulate the system and move in and take over?
There are too many similarities to Germany in the '20s for many people to feel comfortable - this is how Hitler took power. He never broke any laws, but changed them in his interests as he went along.
I only recently learned that the same destiny is planned for Caricom, and whatever scant accountability the rulers of Belize currently have to the people will be lost.
As we all know, the USA provided the aid that enabled Britain to resist Hitler. But that nearly didn't happen, and if Hitler had defeated Britain and consolidated its hold over the whole of Europe, then it's likely that with Nazi Europe on one side and Japan on the other, the USA would have succombed. THAT's the danger of isolationism.