Question: why should Chinese government be allowed to spread propaganda on Western media freely while vice versa is not .
As for the real answer, so that Twitter and co can give a resemblance of being neutral international internet service, as opposed to being "Western media" company tied to regional interests.
There is no "neutral" here; one side is a wealthy government, the other is an informal assembly of citizens.
Do you also believe that political contributions should be unregulated? Wouldn't that be fair and "neutral"? Of course it wouldn't; it would heavily favor the side with the most money.