If we followed through with your argument than it is valid to claim that China did not exist until I had valid evidence of its existance. It's a good thing I found out China really existed. Phew, crisis avoided.
Pfft, next you'll try to claim that Australia really exists.
But naturally, if there was no tangible evidence of Chinas existence, it would be irrational to believe in it. I am not saying one would not have the right to believe in China, I am just saying it would be irrational. And either way, the belief or disbelief in China would not have a huge effect on your life. However, if you chose to worship China, and live your life by what you
perceive to be Chinas will, that would be even more irrational, and it
would have a big effect on your life. Still, you have the right to do what you want to do. And I would have no problem with that, so long as those who believe in China keep their beliefs to themselves. But eventually the followers of China get self-righteous, and try to force other people to believe in China, try to change laws to promote the belief in China, and even try to get the existence of China taught in schools, even though there is no proof for it. Eventually the believers in China take control of the entire country, and start wars with other countries just because they don't believe in China. And all of this is justified by the sole fact that nobody can prove China wrong.