Right, and Flex could have easily returned the favor by talking about Nasser's failings and personal issues...but he didn't 
There is nothing about Nasser himself that he tries to hide, in his various interviews he's admitted sleeping with Milos' wife, his divorce, and scar tissue. He also said in his interview with Alex23 that he doesn't mind criticism of himself, as long as it is accurate and not made up.
Wheeler was questioned whether Nasser was a good bodybuilder, and if questioned I'm sure Nasser would describe Flex as a succesful bodybuilder as well.
You are also making it sound like Nasser's interviews were all negative, he praised many bodybuilders in them too as well as Joe Weider.
Besides fans always want to know the truth about the "sport" and when one has the balls to speak it he gets criticized?