Thank goodness the fictional future was totally unrealistic
SOYLENT GREEN was capable of scaring the crap out of any American, terrified of that horrifying dystopian future, Hong Kong-like overpopulation and widespread poverty and hunger; the once great United States reduced to the level of a third world country. The implication of the movie was that the rest of the world was in as bad a shape.
Fortunately, the movie presumed many dysfunctional factors that would have to occur for the United States to deteriorate that bad. In reality, people in charge of the government and the economy, private and public sectors would have to collude to deliberately make bad decisions to pull down the country. In reality, the United States has tremendous food production capability and could actually increase its food production if necessary. Only domestic and world food market demand keeps American food production at its current level. Heck, on the news this past week, some American dairy farmers dumped their milk supplies because the market prices were too low.
The movie presumed the American people would breed like rabbits. That was feared in 1973. In 2016, American families have typically shrunk to 2 to 3 children. The number of deaths and population growth in the U.S. almost balances out. It's the net effect of immigration that keeps the population growing, but at a small rate. We think we feel overpopulation but that's because of economics and geography. If you live in Los Angeles or New York City where Americans and foreigners want to relocate there for career and job opportunities then you feel like overpopulation is a problem. But if you live in the interior states of the U.S. where population growth is nil or actually negative, you have the exact feeling. You might be lucky and live in a livable city or state, say, Salt Lake City or Las Vegas or Phoenix or Alberquerque where there's a lot going on there but not a lot of population overgrowth and rising costs of living, except jobs are harder to come by.
In the end, the United States depicted in SOYLENT GREEN was simply unrealistic because the nation is not that inflexible nor non-resilient. The U.S. has too many resources to fall back upon and still vast amounts of strategic depth to end up like that. For all of that, it's not a bad idea for the U.S. to contemplate slowing its population growth because the nation incurs geographic overpopulation and thus pollution and local degradation of natural resources. I mean that people are forced to go where they can find a job and earn a living. This creates hotspots of overpopulation like Southern California, New York City where rents go sky high and costs of living soar. It would be nice to live on one's own huge land spread in the picturesque parts of Colorado or Wyoming with few to no people around, except you wouldn't be capable of earning a living.