THAAD in South Korea cannot stop Chinese ICBMs heading for the US. The most likely hit probability comes from ballistic missiles coming towards it and that ain't a sure thing. Chinese ICBMs heading for the US... not a chance.
The reason why China protests THAAD is because it's more likely to increase tensions and that inches closer to war. Just because some Americans show a disregard for the consequences towards their ally, South Korea, in itching to start a war with North Korea, it doesn't mean that everyone else has to be worse than Americans and they're begging for a war more. Some just don't want a war at all especially so the US can flex its muscles to show-off. Just remember how many said the strike on Syria was really a message to China. Yeah, they're so much of a sociopath that they gleefully proclaim the US killed people in another country that has nothing to do with the North Korea situation just to send a message to China. And recently I read an article of how cowardly China is because they're punishing South Korea, not with killing people, but with boycotts just to send a message to the US about THAAD. They're devils if it's true and shows how much of a coward they are killing people in a country that can't strike back just to send a message to a country that can retaliate.
It's funny how the alarmists when Trump was elected said because Trump and Putin were so cozy that they were going to gangbang China together. Now that they've been proven to be soooo wrong, they've moved on to being alarmists over North Korea. If like Trump said that the US can take on North Korea on their own, why hasn't it happened? The chicken hawks climaxing on the US to initiate a pre-emptive strike... if it's so easy, why don't they do it! People who want a war without thinking about the devastation and lives lost on their ally South Korea alone at the start of a war wouldn't hesitate. Yet they are? It's called fake bravado. The US will be the villain if the US starts the war. If this is China's problem as many pundits say. then why is the US bothering? It's all scare tactics to actually get everyone else to do something instead while for the US it costs the least.