Long-term trends

1. Asian growth rates faster than Western growth rates
2. Decline of the dollar as the defacto international currency.
3. Population trends:
The United States is the only major developed country in the world that has a birth rate plus immigration rate sufficient to generate population growth. Western Europe and Japan are faced with a growing burden of elderly and retired people and with population declines down the road. In those countries the shrinking percentage of working-age people will have to support a growing percentage of retired people. Even China is facing that problem. For many years the Chinese government has imposed a limit of one child per family. Now it looks as though that policy is working to curb population growth. In fact the projection for China is population decline.
It is strange to think, after so many decades of hearing about the dangers of population growth, that the success of efforts to curb that growth could turn out to be a problem. The United States could turn out to be lucky that its population is growing, because that growth could turn out to be a solution to the problem of supporting so many Baby Boomers on Social Security. (Probably not a real solution, but perhaps an amelioration.) If we have more people entering the work force, that's more people paying into the Social Security pot. If we have enough growth, we might not go broke quite so fast. Theoretically enough growth, coupled with some reforms, could even result in our survival.
The people who are campaigning against letting more people into our country are really not doing us any favors. We need more willing and able workers. We need them not just to fund our Social Security checks. We need more dreamers of the American Dream, or simply more people with a practical conviction that they can do better here than elsewhere.
It may feel like there are too many people in the world, but that is more of an opinion than a fact. There are benefits to a growing population, not the least of which is that the alternative to growth is decline.
The supposed negative impact of immigration on the social welfare system may be exaggerated, especially in light of the potential positive impact on the Social Security equation. But in the areas in which the social welfare system is negatively impacted, the better solution would be to cut back on government-sponsored social warfare programs, not to cut immigration. If we made the availability of work (and freedom and opportunity) the main incentives for people to come here, we would obviously still get plenty of people. These things really already are the main incentives, but we could make it more so.
Our best days could still be ahead of us, not behind us.