Who believed in the 1950s that “the American people, for all their diversity, were becoming more and more alike”?

Middle class Americans believed in the idea that "the American people, for all their diversity, were becoming more and more alike".

Explanation:

The 1950's is known to be an era of good times for the Americans, specially middle-class white Americans. They were satisfied with their lives during this era. There was an increase in number of people who could afford 'middle-class' standard of living, as per the government. People owned homes, owned cars and even televisions and washing machines.

Middle class Americans during the 1950's thought that their era was the time of prosperity and there was unity in people.

they insisted that there was not enough time to learn everything.  

explanation:

if they were going to steal the answers that is simply because they insisted that there was not enough time to learn everything.