People who actually have cause to deal with energy balance of the planet understand the sign of energy plenty well. It's like saying that people working in finance don't understand the sign of money, and if we only understood that debts were different from credits, we'd have a whole different understanding of the economy. (It would be true if people were that confused, but they're not.)

Furthermore, your overly-simplistic view leads to ridiculous conclusions, like that the more global warming there is, the better, because it keeps more joules on Earth.

Of course when people calculate the energy on earth, E_earth, the sign is positive with energy in and negative with energy out. It's just that we care a lot more about other things than the potential and kinetic energy of earth, so we do the appropriate calculations for that.