Equation
Lieutenant General
Problem is US could say it was "reacting to others" when it invaded Iraq a second time, and Western allies were "reacting" to others when it exceeded its UN mandate to protect Libyans from Gaddafi. So, if your position is US did whatever it please in Iraq, then you also have to say the same for China in the SCS. What's good for the goose is good for the gander.
But no one is dying from military conflict or exchange of gun fire down in the SCS, unlike in Iraq where Operation Winning Hearts and Minds seems to be giving the local people more instability and violence that they wish Saddam was alive and back in power. So yeah...there is a MAJOR difference. Beside, China just wants her land back and no post WW2 status quo can "rule of law" could deny that.