I recently read an opinion piece that suggests that concerns about human population growth are grossly overstated and that nothing of consequence is going to occur.

Consequently, no serious demographer believes that human population growth resembles cancer or the plague. On the contrary, the United Nations projects a global population of 9.3 billion by 2050 and 10.1 billion by 2100. In other words, it will take about 40 years to add 2 billion people, but 50 years to add 1 billion after that. After world population peaks, it is quite possible that it will stop growing altogether and might even decline.
http://www.usatoday.com/story/opinion/2013/03/05/humanity-is-not-a-plague-on-earth-column/1965485/

If we don't consider the metaphorical cancer or plague comparisons, we still have to examine these projections by the U.N.  Is it really settled?

Unfortunately the answer is no.  These numbers are all based on statistical scenarios that are often simply the result of guessing.

Population projections often rely on less-than-reliable data for the world's poorest countries, especially where violence or other conflict hampers research, Zlotnik said. "We have to guess. Sometimes we're more conservative, sometimes not," she said. "More often than not, we're more optimistic about the future and where the world is going."
http://www.worldwatch.org/node/6038

Even so, it is important to note that the U.N. doesn't merely publish one scenario, but they have a low, medium, and high scenario which attempts to project the likely result of changes in fertility.  However, the most important element of these projects is that no one knows if they are correct.

Current projections have already been revised due to small changes in the original assumptions.

U.N. demographers selected a high, medium, and low fertility rate in 2006 to estimate how many children would be born between the years 2005 and 2010. Three years later, the analysis concluded that the low fertility rate was too optimistic, according to Hania Zlotnik, director of the Population Division.
http://www.worldwatch.org/node/6038

While the effect is presently quite small, it does remind us that these projections are not based on science.  They are merely analysis based on assumptions and then projected out over the years.  If there are errors in the assumptions, then the projection is meaningless.

Similarly the assumptions about the impact of such population growth were also downplayed

A Center for Biological Diversity poll released last week reports that a majority of Americans worry about population growth sparking global warming, killing off endangered species or causing other environmental mayhem. And, they say, we have a "moral responsibility" to do something about it.
http://www.usatoday.com/story/opinion/2013/03/05/humanity-is-not-a-plague-on-earth-column/1965485/

Yet, we find that the very same U.N. director of the Population Division stating the opposite

Yet Zlotnik said that overall population growth "is inevitable." As a result, natural resources such as fossil fuels, timber, minerals, and water will likely be severely depleted in many regions. Population growth also compounds global challenges like climate change and biodiversity loss.

Feeding the world's expanding population will increase water demand 70 to 90 percent by 2050 without improved agricultural methods, according to the U.N. World Water Development Report. This is the case even though many regions are already reaching the limits of their water resources, said the report, which is being released at the start of this week's World Water Forum.
http://www.worldwatch.org/node/6038

We should also be clear that if the population growth of 1995-2000 were extrapolated out, then the numbers would be a staggering 134 trillion people in 300 years, a number that even the U.N. report describes as "impossible".  So, we already know that growth must slow down, but we must still consider whether these projections have many other ramifications, and even the high scenario may prove to be extreme.

Nevertheless, the low and high projections have by 2050 already obtained a demographic and behavioural momentum which will not be changed easily, and which in the longer run will be either physically or politically unsustainable. Given our present evidence on such matters as global warming, ozone holes and increasing water shortages in drier countries, the move shown by the high projection towards 14, 21 and then 36 billion seems impossible. In the longer run even the nine billion people of the medium projection, richer than now, might prove to be destabilizing to global systems or incompatible with the way people want to live.
http://www.un.org/esa/population/publications/longrange2/WorldPop2300final.pdf

However, as the report suggests, there's not much we can do about it, since the course has been set, and all we can do is hope that solutions will be found lest the entire process go sideways and we find out what happens when a species encounters a population crisis.

While any individual may feel optimistic or pessimistic regarding our future, and population growth, we should clearly understand that these projections are not based on science.  They are speculations, regardless of how careful and prudent the analysts wish to be, they cannot know whether their assumptions are correct or accurate, or whether they will hold.

So, "Move along, nothing to see here".