Maybe this wiki can explain the crux of the issue better
Hainan Island incident - Wikipedia, the free encyclopedia
"The United States and the People's Republic of China disagree on the legality of the overflights by U.S. naval aircraft of the area where the incident occurred. This part of the
South China Sea comprises part of the PRC's
exclusive economic zone based on the
United Nations Convention on the Law of the Sea.
........
The PRC interprets the Convention as allowing it to preclude other nations' military operations within this area, but the United States maintains that the Convention grants free navigation for all countries' aircraft and ships, including military aircraft and ships, within a country's exclusive economic zone."
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What the Chinese are doing is grabbing specs of land and extending their boundaries with the ultimate goal of
blocking military flights through the South China Sea.
So when I say the U.S. has no interest in flying over your island I mean the main goal of the U.S. Is free military passage through the South China Sea (as is every other country's military in the region). The main goal is not to spy on some tiny islands you are building.
However if China's ultimate goal is to cut off military passage then of course everybody is going to scream about those islands and how they are not "legit" and how the 9 line thing is ridiculous. Of course a ruckus is going to be made.
If you claim your interest in the islands is only because the resources around them are deservedly yours.well that's something between you and your neighbors. But if that was the case why are you so rabidly upset over patrols the U.S. has been flying for the last 70 or so years. Do you think we are there to spy on oil rigs you want to setup or something?