What little recall I have of the fairness doctrine leads me to believe that the news organizations didn't have to automatically include a rebuttal of whatever story they presented, but if some person or group wished to rebut their presentation they had to make time available gratis. The burden was largely financial in having to give up valuable air time, so they tended to stay away from subjects or presentations that they knew would be a lightning rod.
Back in the day I didn't even know there was a fairness doctrine until it was gone. I remember that news outlets talked about controversial issues, and they tended to provide different viewpoints, albeit, it was usually obvious which viewpoint they favored. The FCC requirements were only such that controversial topics of concern to viewers/readers were discussed, and positions were presented honestly/fairly in the judgment of the FCC.