who only by moving can balance

Part of that may be a confusion between "one functioning adult" and "one functioning and mostly self-sufficient* household." Two or more people need more groceries than one, but may not need more grocery lists, or twice as many shopping trips. A larger household is likely to use more electricity, but the effort in setting it up and paying the bill monthly doesn't change if the household uses more or less electricity.

*for early 21st century values of self-sufficient that don't involve growing our own food, making our own clothes, or needing to know how our electricity is generated.