Criticism wasn’t confined to the political right. A more populist critique, which spanned the right and left, centered on the glorification of business as an enterprise that was destroying traditional values, stripping individuals of faith and power over their lives—all in the service of industrial elites and an impersonal, alienating system. Racist critics looked at Rivera’s industrial scenes and saw a reflection of an increasingly diverse society. Migration from the southern United States fundamentally changed the demographic makeup of northern industrial cities like Detroit, including (even first and foremost) Ford's factory floors. In addition, after the U.S. immigration quota system limited European immigration in the mid-1920s, more Mexican workers (not included in the quota system) made their way to U.S. industrial centers and elsewhere.
Nonetheless, many critics of the mural project simply could not get over the idea that a man like Diego Rivera, a Mexican “communist” and a representative of “modern art,” a man who gestured to the organic unity of indigenous and European cultures, that this man would be the one to represent the soul of Detroit to the world. With the continuation and intensification of anti-communist sentiments in the 1950s, the Detroit Institute of Art felt compelled to post the following disclaimer at the entrance to the Rivera's murals:
Rivera's politics and his publicity seeking are detestable. But let's get the record straight on what he did here. He came from Mexico to Detroit, thought our mass production industries and our technology wonderful and very exciting, painted them as one of the great achievements of the twentieth century. This came after the debunking twenties when our artists and writers found nothing worthwhile in America and worst of all in America was the Middle West.
Rivera saw and painted the significance of Detroit as a world city. If we are proud of this city's achievements, we should be proud of these paintings and not lose our heads over what Rivera is doing in Mexico today.