I look at it this way: change is not going to be forced on the Chinese government by US corporations. That can only come from the Chinese population (with possibly a small assist from foreign governments). So what's the best way to help their citizens with changing the government?

I believe the best way is to make them prosperous and informed; people who are hungry or worried about their job are less likely to question the political status quo. Are US corporations helping with either of those? Not much with the latter but I believe more trade helps the former, as long as it also doesn't make it easier for the government to oppress the Chinese population.

Is there much of a difference between US corporations doing business in China and the rest of us buying inexpensive goods from Chinese companies?