The issue is not growth, which is a consistent characteristic of the American Republic, but the disparities that are likely to result in income, education, and ultimately, opportunities. Most of the newcomers are immigrants, and are poor and have less access to education and other opportunities. They are also likely to settle in concentrated areas within 50 miles of the coasts, which will exacerbate the problems we experience (but tolerate) now: sprawl, traffic, and congestion.
The other problem is the drain of our natural resources, most significantly water.
The WSJ nevertheless suggests that immigration and growth are positive, and reflect a thriving economy:
In short, those immigrants are going to be paying my (and others') social security, and keeping economy moving forward. I'm not thrilled about the sprawl, but that's a problem we should be dealing with now, and regardless of how many people come to the U.S.
Most demographers and economists agree that the economy probably can handle the growth -- and may even need it. The U.S. population has grown 50% since 1967 when it hit 200 million. But the size of the economy, as measured by the production of goods and services, is up 217%.
Baby boomers are reaching age 60 at the rate of 8,000 a day and are leaving the labor force even faster. That retirement-age population will grow 120% over the next 35 years, while the working-age population that will be available to replace them is expected to increase just 20%.