The argument is self-evident. Businesses need sales to make money. By refusing to allow them to export, you artificially limit the sales they are able to make. Businesses with fewer sales make less money, businesses that make less money employ fewer people. People without jobs tend to have problems securing food, water, and shelter, and start to get angry enough to topple governments.

Sometimes they win, sometimes the government just kills all the angry people, and you end up like North Korea or Russia under Stalin (or China under Mao).

There's also the fact that China is an aging population and is structurally incapable of having enough children to create a self-sufficient consumer economy, unless they suddenly develope a love of immigrants.