I agree with you on population growth being necessary to grow our economy.
We are in a position to be fairly picky on who we let into our country, and it should be the best & brightest people that the world has to offer. The notion that we, for example, were at any point in history totally cool with whoever came through our southern border or that was our official immigration policy is simply false.
Again I say to you that letting in everybody all the time as you suggested would have significant negative consequences. You want a litmus test for that? Name one country in the world that has that kind of immigration policy.