Even commentary pieces must be built on a firm foundation of unassailable facts. To convince a reader that your opinion has merit, you must have a higher amount of stored credibility because you are risking drawing down on it with every subjective or opinionated statement you make. Your credibility is taxed in direct proportion to the degree of outlandishness that each such statement contains.
For example, each of the following statements puts more of a strain on the author's credibility because of the increasing deviation from mainstream opinion. 1) We should subject anyone coming into the United States from a country of special concern to a more thorough search when boarding an airplane. 2) We should apply a more thorough search to anyone who fits the physical and behavioral profile of previously identified members of a terrorist group. 3) We should subject anyone of Arabian descent to an extended search. 4) We should deny U.S. entry to all foreigners. 5) We should nuke 'em all.
Each of those statements requires the writer to make a much stronger case built on a foundation of facts strong enough to support the authors' opinion, until you get to a statement like the fifth one that is entirely unsupportable and transforms the commentary article into a rant regardless of how much credibility the author has banked with the rest of the article. Carl Sagan may have said it best when he said "extraordinary claims require extraordinary evidence." That applies not only to scientific endeavors, but also to news commentary.
Readers understand that news commentary contains subjective statements based on the author's opinion. Good commentary leads a reader down a logical path. At first, the path should seem like familiar territory to the reader. They should feel as if they are walking on a firm grounding of familiar facts. The author can place plausible opinions in among the facts, like a will-o-wisp drawing the unwary reader deeper and deeper into the writer's forest of logic. The best commentary will take a reader to an unfamiliar destination, sympathizing with the commentary writer's opinion, without them ever realizing they left their old familiar path.