title: Why props in React are read only?
body: <p>The React documentation says: 
  <code>React is pretty flexible but it has a single strict rule: all React components must act like pure functions with respect to their props.
  </code></p>
  
  <p>Why is that?</p>
  
  <p>I guess that if you change directly the value of the props, the component does not re-render, that's why we must use <code>setState</code>. But I still don't understand the reason behind this. Why components must be like pure functions with respect to their props?</p>