What if everyone were the same? Stress the two advantages of everyone being completely equal.
If everyone was of equal strength, looks, and intelligence, etc., there would be less feelings of inadequacy, envy, and jealousy. If everyone was equal in every way, everyone would have the same thoughts, bodies, movements, tastes, preferences and so on. So, with everyone having the same preferences in terms of sexuality, music, culture, movies, etc., each person would have no problems relating to one another. With so many shared interests, it would lead to easy conversations in which everyone was in complete agreement. And with the mental distractions described in this short story, people would be generally unaware that they are being conditioned in these ways. So, they would not wonder about an alternative society in which people are different. Any such thoughts would fade away with the onset of a mental interruption and they would return to the blissful ignorance of living in complete equality.
But clearly, Vonnegut is making the opposite case. Such complete equality would erase difference. And without difference, meaning itself is lost. Simply put, if everyone is the same then there is nothing unique about any one person. Think of this etymologically. If every noun looked the same and meant the same thing, then there would be only one word. This would fundamentally eliminate meaning. "What is a bear?" A bear is a bear. I am you. You are me. There is no meaning because there is no difference between things. And in terms of the self, individuality is lost. The sense of self is lost. And with a society which embraces total equality, there would be no impulse, motivation, or intent to improve one's self, mentally or physically.