Why didn't Truman want MacArthur to eliminate Communism in China?

Trying to eradicate Communism in China could have resulted in a very costly war. MacArthur was a little too "forward" as a leader, but he was successful nonetheless. Seeming as how the U.S. was already in an extremely expensive war with Korea, starting another war could have easily sent the country into a recession. Additionally, China was an emerging superpower at the time, so there was no guarantee that starting a war with the Chinese would be easy to win.