I do think it's true that researching this decision must have been awful back in the day. I think a lot of parents probably resorted to silly reasons
There was information available in print, at least after WWII. Most families also relied on the advice of the family doctor and occasionally asked family and friends for guidance.
An enormous influence on postwar America was Dr Benjamin Spock's bestseller,
The Common Sense Book of Baby and Child Care (1946). In the section on newborns, Spock discussed circumcision. He said that if you have your child circumcised, you'll need to tend to the wound for a few days or weeks. If you don't have your son circumcised, it's important from Day 1 to retract the infant's foreskin and clean the glans. He noted that this is painful, and possibly bloody, and rather unsatisfactory for both mother and baby. On balance, he wrote, his thinking is that circumcision was "a good idea, particularly if the other boys in the neighborhood are circumcised; this helps a boy grow up to feel 'regular'." (Code back then for not a weird loner and not gay.)
You have to remember that this book was the "bible" of child-rearing in the 1950's and even much of the 1960's. It sold millions of copies. Even if you didn't have a copy, it's very likely you knew someone who did, and they could tell you what Dr Spock's advice was. My parents had a copy on the shelf for us kids to read. Circumcision was even discussed (advocated) in
parenting magazines going back to the 1930's and 1940's.
Baby and Child Care had an enormous influence on the rapid expansion of circumcision in the United States. Forty years later Dr Spock had
changed his mind completely, but the effects of his earlier writings were already well-established among the medical profession and among parents.
Even so, circumcision was scarcely discussed in polite company before the emergence of the internet, even as it occasionally came up in magazine articles. This lack of openness and controversy is doubtless part of what fueled the rapid rise of US circumcision, along with nearly every medical plan paying for it. The web has changed everything, in that someone sitting at home can now learn what thousands of people think about a given topic, accompanied by video. They can add their voice to the discussion. One important point that has come from this openness is that the idea a boy will be traumatized, or even bothered, that he doesn't share the same circumcision status as his father or brother is pretty much a myth. If it weren't, wouldn't a whole generation or two of circumcised boys who grew up with intact fathers have been impacted? Why should it only be an issue the other way around, to feel "different" if you're intact? Makes no sense.