A friend of mine brought this to my attention explicitly: kindness is not an inherent trait, but a practiced skill.
Knowing how to be kind to a specific individual requires learning, knowledge, awareness. There are good universal baselines (don’t punch someone in the face, don’t insult or degrade people), but as you go further, the details matter.
And that involves avoiding presuming what will care for the person, what will improve their life. Life is a game of imperfect information, so we’ll never be perfect or get it all right, but that’s a lame excuse to not try at all.
*Be* kind. Or if you can’t, at least don’t justify continued unkindness/harm by refusal to learn what actually works in a given situation.