Should developed nations encourage immigration from other countries?

There have been a lot of discussion and debates about immigration. I think that developed nations should encourage immigration from other countries for the following three reasons.
Firstly immigration make the population of developed nations increased.

For example developed nations have a concern about the population reducing. There are many young people in other countries.

Developed nations solve this problem of the population to accept immigrations more.

Secondly immigration make the nations more powerful.

For example in U.S. there are many immigrations. Because they work hard to earn enough money, their activities make the country wealthy.

Immigrations are the one of the main resource to develop the nations.

Thirdly developed nations can invite intelligent people continuously.

For example Singapore give immigrations who have a high skill and technology working VISA. Singapore also accept immigration who are rich to live there.

The strategy of immigration make the nations actively

In conclusion,For above mentioned three reasons , I agree this theme.