Because no one can point to any economic or social collapse that had anything to do with excessive immigration that was caused by the immigrants themselves. If something has no proof of being harmful and has been going on for centuries, what right does anyone have to arbitrarily limit it? People's talk of unwashed masses just shows it is based on fear alone.
Caps actually produce an uneven spread of immigration. Once one country starts a cap then more immigrants go to a country without. If you apply this at city level you must calculate an arbitrary cap for every settlement until the only way to reach an even immigration pattern is to cap every town in every country.
Simply eliminating caps across the world would spread immigration more evenly. Unless you honestly believe that all immigrants on earth are somehow magnetically attracted to one particular country which is nonsense.
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Just like all bars, restaurants, & schools are as popular as each other! You continue to make ridiculous assertions.
People immigrate for self interest to enhance their prosperity, or lifestyle, & will go to whichever country will allow them in to achieve this.
Immigration is capped to protect the domestic inhabitant's lifestyle & prosperity. Where there are shortages in particular skills & labour, immigration is always actively encouraged from those who fit the bill. And BTW, since the 60s, only about 15% of US immigrants have come from Europe.
Where immigration is unmanaged you have profound social issues. Taking the UK as an example, there are some schools where there are now pupils speaking up to 25 different languages - none of them English. How does a teacher teach to pupils who can't even understand each other?
Then you have the obvious budgetary considerations. How do you house, medically provide for, employ, give welfare to, feed, & police unmanaged immigrants, especially when there were no jobs available to begin with?
The ending of UK border controls led to vast trafficking of Chinese, African & Eastern European indentured workers, including a massive rise in trafficked slave prostitutes, who now seem to form the majority in that profession. Ignorance of social & cultural domestic boundaries have led to the wholesale breach of laws, which only leads to resentment from the original inhabitants.
I've not even mentioned all the other criminals, rapists & murderers fleeing their own countries, entering the UK unchecked. 85%-90% of all murdered police officers in the last 20 years were killed by illegal immigrants & former asylum seekers.
All of this has to be paid for. It can be when it's planned & managed, exactly how do you do this when its not? Its chaos. All communities have a critical mass & a tipping point because the social & physical infrastructure can only handle so much. Depleted resources, chronic living conditions & a poorer quality of life would be the result of the fiasco of your policy.
Furthermore, I once again urge you to look at the immigration laws of various countries - it's not like Europeans or Americans can easily move anywhere else either to non-western countries. You can't even own a house in many (e.g India, Vietnam)!
Why don't you go out, buy a bundle of beer, invite 20 people for a party, then advertise the event on Facebook, with your address, whilst mentioning the free beer.
See what happens! FFS go on a management course, or do something that actually makes you learn about scarce resources, budgeting & planning.