Of course, in LA Santa Monica beach is the rookery of bums. Although by itself this is preposterous, the percent of poverty is relatively small and it doesn't present an existential threat to the USA. Many of these people also don't want to work as they get free food distributed, and the special housing is being built for them. If you ask American bums to immigrate to any other country they will refuse.

In poor ends of the World, most of the population of entire countries are in poverty. That means that most of population wants to immigrate or destroy the natural habitat of plants and animals by cutting down equatorial forests. That endangers not only these countries but the entire World. And we cannot stop them as these are their internal policies. Therefore the only thing we can do is to educate them and teach them how they can help themselves.

For example, Bill and Malinda Gates work on eliminating malaria in the entire World. Also, they try to solve the problem of contaminated water by offering self-maintained toilets. If more people will do this in poor countries there will be fewer attempts of illegal immigration and more poor people in the USA will get jobs that otherwise are filled by non documented workers.