A volunteer at a food bank ladles soup. They're kind to the people in line. They smile. They remember names. They go home tired in the satisfying way. On the drive home, there's a small warmth. A sense of being, this evening, a good person. The warmth is real. The volunteering is real. The kindness is real. And, K would add, the fragment is also real.
The volunteer has built an identity around being kind. The kind person needs an unkind person to recognize themselves against. Not consciously. Not cruelly. The identity kind person couldn't exist without a category of people-who-are-not-kind maintained in the background. The food bank itself draws a line. Those who serve. Those who need serving. The small status difference between them, never named out loud.
This is where K loses most of his audience. People are willing to consider that the patriot and the believer might be fragments. Those examples can be dismissed as someone else's problem. They aren't willing to consider that being a good person is the same mechanism in a more flattering costume. But it is. A virtuous fragment is still a fragment. It still has an inside. An outside. A posture defending the inside.
K wasn't saying don't be kind. He was saying don't become a kind person. Don't build an identity around the kindness. The moment kindness becomes an identity, the kindness gets put in service of the fragment. The fragment has just acquired a more durable defense than the patriot ever had.