This question does not have a simple solution written. So I am copy pasting user ODST117 solution to this.
Social critics say contemporary journalists are cynical and that negatively affects the well being of society. Commentator says that is absurd because journalists have always been cynical and says today’s journalists are more restrained (probably less cynical) than before. Commentator is refuting the claim that journalists being cynical has a negative effect on the well being of society and his justification is that they’ve always been cynical, so if they did harm society’s well being, it would be widespread and noticeable (I know this is a stretch, but it is necessary). But he overlooks the possibility that maybe the cynicism has always had a negative effect on society, no matter how small (Notice they never quantify "negative" here).
I think the commentator is trying to support his point by trying to trick you into questioning the proportionality of the relationship between cynicism and societies well being. But we have no information to question this relationship.