Here is the sort of thing we face when reviewing comments on our stories: A commenter on our recent story on immigration made some reasonable, intelligent comments. (In both cases, that is unfortunately rare.) He pointed out that the estimate for spending by immigrants in the country illegally may be inflated by assuming that they spend at the same rate as Americans. The immigrants he has known are frugal and send much of their money back to their families abroad, he said. Then he raised some basic questions about immigration and said immigration has accounted for more than half of the country's population growth in recent decades, which, according to this study by the Pew Research Center, is true.
But in the same breath, our commenter said the U.S. population is growing exponentially, which is not only false, but the opposite of the truth. The U.S. population has been growing slowly, by less than 1 percent a year, since 2010. From July 2015 to July 2016, the U.S. population had its slowest rate of annual growth since 1937, according to this story in the New York Times, which lays out all the figures.
So, we approved the comment, since it's thoughtful and most of what the commenter says is true. But one statement, put forward as fact, is incorrect and misleading. This sort of thing happens all the time online. People mix fact and fiction, but present the whole mix as fact. And readers believe it, because it contains some fact, or is mostly factual.
Believing incorrect things can lead to pushing for policies, such as restrictions on legal immigration, based on false assumptions. If you believe our population is growing exponentially, then that bolsters the case for immigration restrictions. But if you believe the truth, that our population is growing at a historically slow rate, then you may come to a different conclusion.