I suppose someone a few hundred years into the future could make similar observations about the “Church” of today where it is common to have pro abortionists, gay marriage supporters and where a large portion of the congregation supports contraception and, perhaps, even euthanasia, under some conditions, despite the fact that Church teaching on all of these opposes those positions. Has the Church changed is position on any of those issues? No. How do we explain the fact that those sitting in the pews oppose the Church’s position and yet claim they are “Catholic?” This even applies to some of the hierarchy that promote their heretical views as catholic.
The thing to do would be to engage in deeper inquiry into what the magisterium of the Church actually held, where and why dissenting views were voiced and how those views were tolerated or dealt with. Abortion supporting “Catholic” politicians, for example, are tolerated in Church congregations, ( a contentious issue among many Catholics,) yet these politicians are clearly in opposition to Church teaching. These Catholic politicians are in a similar boat to the slave owners of the past who may have been tolerated in the pews but were not representative of the Church on that issue. Their mere presence is not to be taken as indicative of what the Church teaches.
Hopefully, future historians will not have the same “impressions” concerning the position of the Church then as you do today about its position on slavery two hundred years ago.
I guess the answer to your question is that we need to look at how moral views can be very diverse and not rigidly policed as an aspect of personal responsibility. The Church’s authority and responsibility is more one of teaching and clarifying rather than policing.