The "theological reflection" that happened was after the true effects of the birth control "pill" became more known. I doubt more than a handful of people (probably doctors and chemists that worked to invent it) knew that there was a secondary purpose of the pill which was to make the uterine lining inhospitable to implantation of a fertilized egg, should it occur. No pill has been invented that can stop ANY egg from being released and fertilized and it does happen, though no one knows for sure with what frequency. Until that fact came out, nobody understood that a mini-abortion can take place in women who use hormonal contraceptives.
I think it is disingenuous to accuse Evangelicals of EVER condoning premarital sex or adultery. That has always been considered a sin as is abortion. It is only when the life of the mother is threatened - meaning she will die (as will her baby) - unless the pregnancy is stopped, is taking the life of the baby warranted. In those cases, it is not really an abortion but a lifesaving surgery that unfortunately results in the baby dying.
Other than before clinical trials were even begun, there was never a time when "a handful of people" knew how such "contraceptives" worked nor was there ever a time when anyone who wasn't deliberately hiding from reality didn't know that such "contraceptives" were reliable only because their primary function was to ensure conception would nearly always result in an abortion. Any woman taking "contraceptives" of that sort who has had a late period followed by "heavy flow" has had a "contraceptive" induced abortion and that is exactly what formulations like "the Pill" have always been intended to do.
Any time after the early sixties, there is no way anyone honestly interested in the moral implications of such "contraceptives" could avoid knowing that endorsing their use was endorsing abortion. Going along to get along was and is the overriding "theological" dogma of those "leaders" who approved of such contraceptives, period. Any time after mid-1971 anyone who "didn't know" didn't want to know just like anyone who "didn't know" about the greatly increased cancer risk didn't want to know.
Starting in 1960 Barbara Seaman made a LOT of noise over the Pill causing abortions and greatly increasing the risk of cancer for those who use it. Her activism, articles, and especially her testimony before a Congressional committee not long after her book, The Doctors' Case Against The Pill, came out in 1969 are what led to all prescription and OTC medications having the lengthy and detailed package insert that is now required.
She was absolutely an abortion supporter but she was also absolutely against women taking a "contraceptive" that worked primarily by causing an abortion. She considered that point not being made clear on the outside of every package a deliberate violation of "informed consent" laws and therefore she fought the rest of her life to have a warning label clearly stating that a product worked primarily by causing abortions on any contraceptive formulation like "The Pill". She also wanted a warning about the huge increase in cancer risk associated with regular Estrogen use and the negative effects of multiple abortions whether they were done by invasive means or induced by a "contraceptive".
There was never any question of how such contraceptives work, only a question of whether the average consumer should be well informed. Overall I'm no fan of Barbara Seaman, but was right about "the Pill" and similar "contraceptives". She paid a heavy price for fighting for women having full knowledge of how "the Pill" worked, a battle she won as far as having the facts clearly stated in the package insert but lost with regard to the warning label on the outside of the package. Given the fact that warnings about even trace amount of peanut oil are stated on the outside of food packaging, she wasn't being the least bit unreasonable for wanting multiple clear warnings on the outside of each package of contraceptives that cause abortions.
When in clinical trials formulations with a much higher Estrogen content which actually did mostly avoid conception caused negative reactions (including several deaths) so often, pharmaceutical companies revised their goals and accepted abortion as the primary way to avoid having a child rather than sticking to their original goal of avoiding contraception in the first place. In spite of the questionable legality of inducing abortions at that time, drug companies were intent on marketing an oral contraceptive. A good bit of the big money behind the push to legalize abortion was directly and indirectly from pharmaceutical companies still worried about their legal liability for marketing "contraceptives" that routinely induced then illegal abortions.
The pill as a theological reflection didn’t come first, but in our lives the pill did make us think. When it became apparent that it wasn’t safe for my wife to use, we abandoned it. But, it did cause reflection.
The physical danger it presented taught us that it was not “natural” or healthy for my wife.
And that is a starting point for a theological reflection.