It's true, but uninteresting. Insisting on this truth is harmful, because it makes an assumption that people can just choose to eat less without any negative consequences. People love pretending that calories in is simply a matter of rational choice, not a complex result of our inner machinery.

We are biological machines, and the amount we eat is biologically determined by our bodies (assuming food is widely available). We can somewhat influence that with rational thought, but to a limited degree, just like we can choose to breathe in faster or slower, but we can't maintain that for any length of time.