[smac8]

Not sure what you mean on component state, as I've never heard anyone say that is explicitly harmful, but I think what you might be getting at is the principal in react of creating MINIMAL state such that any logic - for example something that renders an item - can compute off that MINIMAL state, rather than creating a new state that's the result of processing that basic state. The example given in Thinking in React[1] is having an array in state, but computing it's length somewhere (say in render), rather than making the length of the array also part of the state.

On this note, I find that I rarely use state in child components, because as much as possible I have functions that compute values off props and simply return that where I need them, rather than storing them as state variables.

[1] https://facebook.github.io/react/docs/thinking-in-react.html