So let me get this straight. If somebody shows a flag which represents severe oppression that's freedom of speech. 
But if somebody else says 'I think it should be burned' that is not freedom of speech. 

You didn't think this through did you? 
He may have the right to hang that disgusting flag. But I for damn sure have the right to call it disgusting and suggest the only thing it is good for is getting the braai started. 
You really need to read the article properly and stop skimming it. That's the whole point of the article. That no concept of freedom involves freedom from criticism. No right you may or may not have entities you to exercise it without the risk of society disapproving. 
You may or may not have the right to fly this flag. But you have no right to stop people calling you an unevolved, racist, throwback if you do.