There are two schools of thought when it comes to power: to gain power, or give power.
Power itself is not evil. People who choose to use it for evil ruin it for everyone.
Ancient civilizations had technology much more advanced than ours. The difference is they shared that energy, like Luffy would, while modern rulers act like the Celestial Dragons, and use power/knowledge to control and abuse people.
Alabasta said it best: a nation is its people. Power is not evil. We all come from the same Light/Atomic Matter. What matters is how we use our power.
You are totally right. The more power you have in a country, the more evil you'll have fighting over it. Power is not evil. Desire to use power for evil is wrong.
The USA has so many resources and land, and... my people use it for evil. The land, the oil, the gold, are not evil. The Vearth is not evil.
We have let the world be abused, and the world around us is suffering because of it. The earth, air, water, and fire are all God. God is the life before us, not the words liars told us.
A good nation gives power to other nations, and too many modern nations just want to steal and kill. Oda's not perfect, but I respect his overall message: people with power should help others.