What I don't get is why the React guys don't just call the passed functions with 'this' being the component, which seems like the most common use case. If you need to override this, you could indeed use bind (it's not overridable after that AFAIK so no logic is required from React side).
Because it's really _not_ "the most common use case". Components often pass down callbacks through multiple levels of children. A basic example would be a Form component that renders something like:
<Button onClick={this.onFirstNameChanged} />
The proper context for `this` is the Form, but the callback is used in the context of the Button.
Besides, one of the main tenets of React is that "it's just JS", so normal JS rules apply. Now, the old-style `React.createClass()` method _did_ actually bind all "class methods" to the component instances so you didn't have to worry about it, but that wasn't typical JS behavior. ES6 classes don't auto-bind their methods, so neither does the `React.Component` base class.
The current recommended approach is to use the Stage 3 Class Properties syntax, which allows defining class methods as arrow functions that are auto-bound to the proper class/component instance. Very long-term, the React team intends to introduce a "stateful functional component" API that doesn't have to worry about class instances, but that's going to be a while. (There are some assorted userland experiments with writing "`this`-less components" as well.)
That's a good question, I never thought of that. Maybe while rendering they don't have easy access to which component is "this" due to the recursive algorithm they probably use? That's my only guess.
