The only two posts in this thread to explicitly mention the 50s were critical of the childbirth practices of the time. (I personally think they were very far from ideal.) While some people talked about traditional childbirth practices, there is no reason to think that "traditional" refers to the 50s.
For most of Western history, not to mention the majority of other human cultures, men did not get involved in labour and delivery. Our society is a historical anomaly in this regard. It is not surprising that this leads some people to question the current practice. What is it about our society that makes us different? While I see nothing inherently immoral about husbands being present, it is not normal.
Well, unlike Church traditions, social traditions like those don't necessarily have any kind of authority behind them. For the longest time, people used to smoke cigarettes everywhere too. I remember seeing a retro commercial about how "4 out of 5 doctors smoke [a certain brand]", and one of them was lighting up right next to a patient. Some social changes can in fact represent true progress. We really have to avoid this tendency (common among Traditionalists) that (simplistically) old=good, new=bad. That's not ALWAYS the case. People were subject to Original Sin in the past too, you know.
So we need to dig into the WHYs and not just cite this practice as normative in principle. As Pax pointed out, in the past women had more female relatives in a support structure, and would perhaps have been more comforted by having around them people who actually had gone through childbirth and knew what she was experiencing. Someone mentioned that women perhaps would not want their husbands to see them all disheveled. Neither of these is super compelling. For a woman (and it's most women today) who lack those support structures, what's left is some notion that the woman would retain her dignity more if her husband didn't see her like that, or that the husband might stress her out (not true in the case of all men) ... none of this is particularly compelling. I know quite a few men (myself included) who are far more calm under pressure than their wives. Traditional practices certainly carry SOME weight behind them, but they need to be deconstructed to understand the rationale behind them, and whether those pertain to the historical context or other circuмstances that are subject to change. Or, another consideration, was it believed that men, after witnessing childbirth, might be somehow less attracted to their wives and less inclined to have marital relations ... and to have more children in general? Not sure.
Most women today would be offended if their husband weren't in the delivery room with them ... except for those who have husbands who "freak out" ... and those women probably wished that their husbands weren't quite so pusillanimous and would lend them the strength that men are supposed to support their wives with.