Why, according to the source, was the NEP viewed as a failure by the communists?

The NEP, or New Economic Policy, was perceived as a failure by many communists because it allowed for a degree of capitalism that contradicted the principles of Marxism. While it was implemented to revive the economy after the Russian Civil War, the rise of private trade and small private enterprises led to concerns that the socialist ideals were being undermined. This shift sparked fears that it could lead to a class divide, where the peasants and small capitalists regained too much power and wealth, threatening the communist vision of a classless society. Moreover, Stalin and his supporters viewed the NEP as a retreat from revolutionary principles, paving the way for more state control and the collectivization of agriculture in the future. This created a divide within the party, leading to debates over the direction of the Soviet economy and the future of communism, ultimately resulting in the more radical policies that followed.