Immigration

Mass immigration from Africa to Europe and USA is not totally unproblematic.

The most common reason why the citizens of rich countries don't like it when poor Africans or Asians want to immigrate to their country, is simply money. The country has average standard of living X, and employment Y, and salary level Z. Mass immigration of many poor people would cause the unemployment to rise, and the average standard of living and salary levels to go down.

(In a free market economy this would happen quite certainly. Not so certainly in a planned Socialist economy, which would be able to plan work for the new immigrants more effectively and equally than a free market economy wants to do. But Europe and USA are free market economies, not planned Socialist economies.)

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This was only one problem. Another problem is territory, natural resources etc.

It is not perfectly sensible if some African or Asian dictators treat their citizens very badly, or destroy their national economy with corruption and bad economical planning,
and then:
great masses of people from these countries abandon their home countries, leave behind their right to the natural resources and land area of their home country, and immigrate to already densely populated European or American countries.

This means that the bad political leaders of Africa or Asia are REWARDED by the population going away, which means that average amount of natural resources and land area per citizen rises in the country. Likewise, the more successful political leaders of Europe and USA are PUNISHED by receiving masses of new population and problems, which will reduce the available natural resources and land area per citizen in the country.

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An optimal situation would be something like free "competition of governments": if government X is taking good care of their citizens, and government Z is doing bad and corrupt work, then the people who want to live under government X would simply get their land area moved under the control of government X, without anyone migrating anywhere.

I probably made a big mess of these thoughts, but the main points are:
- mass migration of people from country to country causes:
--- ecological problems of population density, natural resources, water resources etc.
--- practical problems of economical planning, employment planning, housing, etc.
A better alternative would be economical and political development in the countries where political or economical circumstances are uncomfortable, without mass migration from country to country, even if a small number of individuals would choose to move around a bit.

The practical problem in this scenario is the fact that the existing regimes in Africa and Asia are not so easily changed, many of them are actually backed up by USA, and even if not, they can have a strong military grip of their population, and rigged elections or monarchy to ensure continuation of their power in the country.