Well, there are some countries that might face such an issue. But, I am not informed enough to know of any. From what I know of due to it's small size countries such as the UK would be the ones I would consider most vulnerable to that sort of thing.
Of course not everyone will use birth control. But, I am sure that enough will that on a resource perspective in the mid to long term there shouldn't be an issue. Although, there is a cultural issue. First, is the danger that immigrants could lose touch with good elements of the culture of their original home. The other is that an excessive number of immigrant from a single country with a strong culture can often affect the broader culture they immigrate to in negative ways.
Of course a sudden influx of a large number of immigrants could be taxing to a country in the short term if they were not prepared.
I am hugely against illegal immigration in particular in the US because the system in place today makes it easy for illegal immigrants to be used as slaves illegally in the US. And then the threat of Deportation is amplified and used so that these immigrants have little to no protection. And any attempt escape from their slavery would just result in being sent back to the horribly run country they came from.
On the policy level, having an effective way of managing legal immigration is very important. From what I can tell the historic and current US system doesn't work. I don't really think this is the right thread to discuss what form of immigration policy would be best for the US in the present considering this thread's focus on history.
There is a potential issue of resource shortages. Particularly when it comes to things like welfare, and hospital system. In the US, the destitute are treated free for life threatening injuries even if the don't have insurance. Even for non-citizens or illegal immigrants. But the cost of those treatments is carried at the lower levels. So, when enough people move into an area smaller hospitals either have, to get more money from somewhere or reduce costs by cutting things the hospital considers less important. Or raising costs for uninsured people to get health care for non-life threatening things. In some cases, Immmigration can have negative effects on a community. I think 100% open borders with no requirements for immigrants could have a lot of negative effects. There are also many countries where misinformation about how immgration works are actively spread to encourage people who would normally immigrate legally to do so illegally so that they can be exploited. A bad immigration system can easily result in immigrates being worse of than what they were in the country the came from.
The 10 countries with the highest GDP have over 60% of the total GDP according to the World Bank.
World Bank Source
So, they have a disproportionately large share of the world's wealth. Just China and the US have 40% of the worlds GDP.
So, if immigration causes the richest countries to have to split their wealth further, there should be plenty of wealth to split. There are some nations that really can't afford immigrants. But, most of the ones I know are not the ones I typically hear of people getting riled up about it in. Although, if you think that a war between the US, and china is coming then that gives a lot more reason to care about the relative strengths of the two. But, a lot of things that might give an advantage in case of war are pretty unethical.
I think the most important problem regarding immigration to address is the brain drain problem. But, that is not the usual aspect I see tackled when it is brought up.
I think it is currently a pretty bad time to tackle immigration issues due to the current economic climate. Although, discussion might still yield something of use in the future.
I also think that comparing something to colonialism is mostly useful to point out when bad things are happening. I think that comparing the CCP belt and Road Initiative to colonialism might be useful.
Offering countries that might be tempted by such a deal better deals could be a good idea to curb chineese influence. But, I am peesimistic about whether it will actually improve things for the nations given the deals. From what I can tell in the vast majority of cases, CCP money is a trap for smaller countries. Maybe US money might have less negative consequences? I think that whatever deals happen the Big US corporations will manage to get in on thm in a way that allows them to benefit at someone else expense. But, I guess that having you countr trapped by US companies might be better than being under the thumb of the CCPs authoritarian regime.
Also, I agree that this topic is no longer productive. The only reason I posted this is because I wrote it back when I felt like it still was.