If this was the best system of man,as you say, they certainly knew that it was wrong.This coupled with the way they went about it was despicable by going to another land and praying on the weak.
The Church did nothing to stop slavery.
The Church was politically weak due to the Reformation,they spoke against it,but it went on deaf ears because making money for the wealthy was more important than people in this system.
praying on the weak. = preying on the weak
For their time, the Founding Fathers were way ahead of everyone else in the world which was ruled by autocratic despots. In fact, compared to their peers, they were extremely liberal, or left-orineted as we would say today.
Unlike any other country, it did away with the official Church, it had an elected president subject to the will of the people, etc. The press was relatively free. The religion was relatively free, the society was relatively free. One could be a deist but not necessarily an open atheist.
Taking of the land from the Natives was not seen as "wrong" any more than racial segragation in the society was seen as recently as 50-60 yeas ago.
The land was seen as a Providential gift to the new settlers, and cliaming it for the Motherland was not uncommon in any society. Natives themsleves fought over land contorl. The westward expansion was seen as a manifest of divine destiny.
Slavery was as much part of life as chickens. It has been there forever. It is biblical. It was not condemned in either Testament.
We can not judge the Founding Fathers for not counting the slaves as "men endowed with inalienable rights" because the Christian God does not condemn slavery. neither does any other god. So, there simply was no precedent.
Slavery was abolished not only in the US but all over the world pretty much at the same time, the 19th century, not as a 'revelation' that it was wrong but because it outlived its usefulness in the new industrial era.
The Church was politically weak due to the Reformation,they spoke against it,but it went on deaf ears because making money for the wealthy was more important than people in this system.
I am not aware that the Church spoke against it. St. Paul doesn't. Christ doesn't. Why would the Church? After all the Church became the state institution just about 1,700 years ago and existed as such in the slave-owning Roman Empire all the way into the 15th century and never raised a serious opposition to slavery.
Neither did the Western Church, as far as I know, oppose slavery actively, but I am not discounting brave efforts by some individuals as a distinct but ineffective possibility. I am simply not aware of any prominent opposition to slavery in either the East or the West.