In real countries, you need to become part of the community in a legal way. You must register, file papers, prove you have work, money to live on, and that you are not going to be a burden on society.
How many illegals crossing the border have jobs, have sponsorship, have money to live on while they integrate? The US is not a welfare "nanny" country. Allowing open borders for poverty stricken people is another way to put chaos in the economy, and destroy the welfare system. It demoralizes the country even more.
In smart, European countries they bring labor in from the poor countries, but do it with full disclosure and no burden on the economic system. What is the point of turning the US into a 3rd world country? Takeover?