If there is more opportunity somewhere else, wouldn't you go? Would you like people standing on the border denying the opportunity to have a better life? Why should the greatest nation on earth not want to help those who strive for better. After all, we are all here because our ancestors went looking for a better life.
You don't seem to understand the law of unintended consequences. The end result of your idea would be that the standard of living of the United States would be lowered to that of Mexico. The people immigrating from Mexico and Centeral America have no idea what self governance is, they are used to guns being illegal, they get their information from liberal sources. Once they start to vote they will vote for Democrats, gun control, and every hand out program on the ballot. They will have no loyalty to this country, they are here for the money. Then You, and I will live on the streets. Broke, hungry, sick and no hope.
It is already starting to happen in the Southwest.