They didn't defend them from a communist invasion. US they were defending their interests of not wanting a communist world because it was a ideological battle. So it happened in Vietnam and Afghanistan in the 70s/80s. US was not going to safe anyone but themselves in a geopolitics war. Same as with what
@langster says. There is fear that China overtakes the hegemony of US and the west and they need to find the negative parts of China, that there are A LOT. so in the west. I don't necessary agree with @langester that china will start a war or not. But who knows who will start escalating the tensions on purpose to start a conflict or starting it with poor excuses to blatant lies. US is a master on this.
It happened with the tensions before Japan's attack in Pearl Harbour, organizing coups around the world, the lies from Iraq war and many others. Taiwan is definitely a factor that could bring china to war first. Then China is accused to have an aggressive stand, but is the US that has an aggressive international stand with China, with bases in south korea, Japan, philippines and Singapore. And they are opening more and more. And they have a fleet patrolling constantly. There is an acceptance that US can do that but not China. Why? I mean, I don't want China either to have military bases, but I don't understand the double standards
In the end is not good vs bad. Is ones interests against others interests. And both are evil nations. I will root for US as is my bouncer though, but I don't fool myself that is the good guy. Paraphrasing FDR, Is a son a bitch but our son of a bitch