There's blame on both sides. Denmark doesn't do a stellar job of integrating outsiders despite ample funding. Likewise there are cultural incompatibilities, such as the handshake-citizenship debacle in a country that has arguably the closest gender equality in the world.
My personal lesson is that immigration is really complicated. I truly believe people should be free to move wherever to realise their maximum potential. But in holding this standpoint you must acknowledge the very real costs incurred.
https://en.wikipedia.org/wiki/File:Total_Fertility_Rate,_195...
Why? Why not improve their local environment to better help them "realise their maximum potential"? (I put your words in quotes because it's not a phrasing I like very much).
Why create a world where people have to move to have better opportunities rather than creating a world where there are better opportunities in increasingly more places?
How can it be bad for immigrants to get more than they put in, but not citizens?
The “immigrants will get more out of welfare than they put in” is exactly how welfare is supposed to work!
It's not a zero sum game.
Are you hoping that it will allow certain aspects of the culture to spread / persist?
If the latter, would it be as good to cultivate those things at home and allow them to spread on their own merit?
Or do you prefer for more people to exist under the national banner for its own sake?
I don't see how it figures that more people packed into the same territory competing for a dwindling pool of resources is good for my country, even if the hundreds of millions of newcomers are eventually "Americans". I support controlled immigration when it benefits our country, but immigration for the sake of growing our population seems monumentally foolish. Housing, education, and healthcare are already scarce resources - let's focus on how to build our country into a better place to live for the people who are already vested in the system. In before "they'll pay for our pensions!" - debunked, more like "we're already paying for their food, housing, clothing, education, healthcare, and children", at least when it comes to illegal immigrants.
Also, for the environmentally-conscious - people moving here, a high per-capita carbon emissions country, from low per-capita carbon emissions country, is contributing to climate change. It's very frustrating to see publications from Wapo, to Time, to NatGeo encouraging Americans to stop having children to fight climate change, while simultaneously supporting high levels of immigration that contribute very significantly to increasing our population.
Which implies American levels of consumption and environmental damage.
Problem 2: it is unethical for rich people to depend on the fertility and then parental obligations of poor people in order to produce new people who will then be taxed to pay for the sterile old rich person. That is asking someone else to do all your hard work for you for free.
Um do you live here? That is basically how the economy works.
How do the people who immigrate here affect the behavior of people in the countries they left behind? Why would they not continue having too many children?
Do you not see the historical irony? Your (presumably European) ancestors had their own countries too. So did the inhabitants of the Americas before white people arrived there from 'their own countries'.
Every country has a starting point, the USA's is just more recent.
The example of Sweden is indicative of what I tried to convey as it has made the "salad bowl" concept part of its constitution which states that the country should "actively promote the distinctive collective identities of national minorities and immigrants" ([1] gives some insight in how things came to be like the way they are in Sweden). In the space of a few decades the country went from being one of the most homogeneous on earth to a boiling kettle of contrasting and often clashing cultures to which the term "mutt" - a mixed breed which has characteristics of all its predecessors - is not applicable as the constituent cultures mostly hold to their own. It is at the interfaces between those cultures tensions arise, sometimes between native Swedes and immigrants but more so between different groups of immigrants.
[1] https://www.jstor.org/stable/10.3366/j.ctt20q22fw.13 ("The Political Dynamics of Multiculturalism in Sweden")