My understanding is that when it comes the US maneuvers in international waters of the South China Sea, the purpose is actually defensive. Part of international maritime law determining the owner of waterways includes considerations for actual control of areas.
By navigating international waters against China's wishes, the US is demonstrating to the international community that China does not control access to those waters. This prevents China from making claims that those waters should no longer be international and instead be China's.
So this isn't the US going off to provoke China (or if you still wish to see it so, at least not for no reason). This is the US exercising rights granted by international treaties in order to prevent China from making effectively false claims to those waters under those same treaties.