Don't get our gov't doing something in the 'national interest' mixed up with doing the right thing, or being the good guy. Don't even be that stupid.
People don't get riled up and angry without thinking they're right about something, and the Chinese are no different.
Here's a little hint for you. In 1937-1945 China lost about 20 Million fighting Japan, and had about 15 million injured. One particular event, known as the "Rape of Nanking", resulted in ~ 300,000 civilians in one city being systematically raped and executed by the Japanese.
Here's one exerpt from someone who was there :
"On December 23rd, Japanese invaders used several dozens of trucks, drove more than one thousand elderly, women and children to the sandbank, and buried them alive in a huge pit dug beforehand. All the victims' hands were tied behind their backs, they could only cry and curse, they had no way to resist."
It looked something like this :
Why do I mention that?
Because one big item about the South China Sea is the dispute between Japan and China is over a chain of islands called the Senkaku Islands, and adjacent waters.
Not to mention, Taiwan.
So lets think about this.
The Senkaku islands, and Taiwan, were taken from China by force in *two* very bloody wars defending against genocidal aggression by the Japanese (yes there was a first, and second, Sino-Japanese war).
China didn't fight Japan being given the islands initially because they were devastated, and dependent on US support. That's pretty much historical fact, in a nutshell.
Now try to empathize, put yourself in China's shoes. I'd be pretty pissed about it, and as my country got stronger, I'd probably expect them to do something to fix it. Wouldn't you? Asia got a raw deal after WW II, all the focus was on Europe. That led right into Vietnam as the US tried to protect French colonial colonies there.
It's a nice little SNAFU left over by Imperial Japan and what was probably some overly greedy Allies dealing with a very weak China 70 years ago.
And it's going to make for one hell of a shit storm over there one of these days.
Do you want US soldiers to potentially DIE to defend THAT??
How about NO. The only reasons to do anything there is to defend a clear US national interest, like oil, or economic interests. That's it. Unfortunately those do exist there.
Like I said at the beginning of this post, don't get confused with defending national interests and being the good guy. That's just stupidity, hypocrisy, and bravado.