It occurs to me that liberals can be authoritarian, too.
That said, I don't think the US bishops, as a group, were hardliners about HV, especially in the ten years that remained to Paul VI. (JPII changed everything, including the makeup of the hierarchy.) The US Bishops' pastoral letter responding to HV, 'Human Life in Our Day', was a moderate affirmation both of the teaching of HV and of the conscience rights of married couples. There were many priests who wrestled with HV as confessors, and many bishops who tried conscientiously to help them do it. I knew one very conservative priest who left ministry because he thought HV was wrong, but he could see no wiggle room for himself as a confessor. Many people remember or know about Cardinal O'Boyle's confrontation with the Catholic University theologians. I don't think O'Boyle was representative of the US hierarchy. I think it's important to note that he was acting not as Archbishop of Washington but as Chancellor of the University.