The assumption that you are making is that if you are plugged into a 30amp outlet, you are using that entire 30amps. Therefore if you also plug into the 20amp outlet, you are using more than authorized and "stealing".
But you are not accounting for the actual usage. I may have two heaters but I can't plug them both into my RV outlets because the outlets are all on the same 15amp circuit breaker. So I run one off the 20amp outlet at the pedestal so it doesn't pop my breaker. But my actual electrical use is still under the 30amps that I'm paying for.
Our electrical rates here have a major increase for a peak period. I can run 2X load during non-peak hours and still pay less than running X load during peak hours. So am I stealing if my greater usage cost is less than someone using less during the higher cost period?