I'm not sure where the usage of the title "Deaconess" originated
Some translations of Romans 16:1 read something along the lines of the following "I commend to you our sister Phoebe, a deacon of the church at Cenchreae" (That's the NRSV bible, but it is not the only translation that reads essentially that way). There is either an early ecumenical council or a local church council at some point that laid out some rules for how many deaconesses a diocese could have (Then using the term deaconess rather than deacon IIRC) and what the qualifications were for becoming one (Something like a widowed celibate or widowed woman over 40, if I recall correctly), which in context appears to be them restricting a pre-existing practice that was previously more liberalized. However, this of course fell out of favor before the end of the first millennium after Christ and one can find things forbidding deaconesses and such.
The debate in Christian circles is largely centered around whether these deaconesses were deacons in the ordained sense who would read the Gospel at mass and so on and so forth just as male deacons, or whether they were unordained female volunteers upon whom a title was conferred without ordination who would do things like assist with baptisms for female converts, as the custom in those days was for adult converts to be baptized naked in a river and there would have been some questions surrounding just what was going on there if it had been naked women alone with a man or several men. I am not sure there is persuasive evidence for either viewpoint, either is possible.
In Catholicism and some similar churches and denominations where ordination is said to be something that creates a permanent ontological change to someone's soul, which is marked forever, the question of whether deaconesses were ordained becomes more significant than in other traditions, even if there became some consensus as to what precisely they did and if the question were to only come down to whether it was an ordained or non-ordained role. Some conservatives to view that the three-fold ordained ministry of the bishops, priests, and deacons is given by God and restricted by God to men and can not be altered by humankind, but the latter part of that preposition would fall apart if female deaconess were proven to have been *ordained*. In theory, this would create a traditional argument that ordination of women is possible theologically and that the decision not to have women bishops and priests is also a matter of discipline, rather than doctrine or discipline, which would make it a discretionary thing that the Church could change at any time versus something that that the Church has no authority to ever allow.
Of course, there are some who would reject the very basis for the argument and simply say that women should be allowed to be ordained regardless of history, and that if there were not historical ordinations, it was because of sexism or people bowing to limitations imposed by sexism or circumstances that are not necessarily relevant any longer to today's Church. At certain times during the Roman Empire, Christianity was viewed as a woman's religion, and restricting ordination at that time to only men could have been a way to combat that, or the Apostles might have simply ordained men because they were Jewish and that was the Jewish tradition, and then had people take it as holy writ when it may not have been.
I think there is often a subtext to these discussions about whether Jesus was simply the end of the discussion on everything in his time on earth, or whether he was pointing in a direction in which things should continue to move. Perhaps, for example, he was including women to a greater extent and in more distinct roles than Judaism and some other religions might have been accepting at that time, and could not push any more *at that time* without limiting the reach of the religion that would develop from his teachings, and we should continue to push to the limits of what our society will accept, which would probably mean ordained women bishops, priests, and deacons.
I think often the traditional point of view is limits our moral understanding to essentially those of 2,000 years ago, whereas a more progressive outlook allows us to advance morally and ethically. Vatican II was I think the first time the idea of doctrinal development was explicitly recognized, which was perceived a major change in it's time and part of the basis of some traditionalists schisming over or complaining about the council, but Vatican II's definition of doctrinal development, while a change from the traditional ideas surrounding the issue, and over all a liberalization, was not quite as progressive as some would have liked either as it did not allow for development along certain lines. Had the Church continued to go in the direction of Vatican II, the next council probably would have liberalized even further, but John-Paul II and Benedict XVI aggressively tried to reign in interpretations of the council and view them through a very traditional lens in many respects, and appointed bishops largely on the basis of finding people who agreed with their theology. Rembert Weakland, former Archbishop of Milwaukee, comments extensively on the difference between bishops appointed by the few Popes preceding JP2's tenure as Pope and that the type of bishops JP2 was appointing in his book and how the newer bishops were less independent thinkers and tended to view themselves more as foot soldiers of the Pope than as co-equals who could have their own opinions as the previous generation (The Pope technically is simply the "first among equals", a phrase which is very vague and gets interpreted differently at different times and by different people). He said the local bishops conference in the United States used to involve a lot of debate and independent decision making, but quickly transitioned to people quoting the latest encyclicals and doing whatever they thought Rome wanted as the older bishops retired and the ones appointed during JP2's 26 year tenure became a large minority, and then a majority, and eventually the entire conference. There was, in his view, a transition from independent thinkers selected for their pastoral qualities to people selected almost entirely for theological agreement who were perhaps less equipped to be shepherds of their own flocks.
