FB and google both have a larger population than china. Censorship by FB or Google is far more harmful/effective than whatever the chinese government does.
Also, would we support corporations right to censor if they were censoring content we disagreed with? Imagine if FB/Youtube/Verizon/etc started censoring lgbt content. Would we still use the "private companies" can do whatever they want argument?
Given how powerful many companies are ( especially monopolistic companies like FB/GOOG ) maybe it's time corporations are required to protect free speech like corporations are required to protect the rights of minorities/disabled/etc.