That was a widely held belief in the USA and people in the church (parishioners and church leaders) were not shy about articulating it. In fact, even the intellectuals throughout the 19th century used the Bible specifically to justify slavery. Many biblical scholars in early America interpreted the Pentateuch as identify blacks as condemned to slavery and morally inferior to whites.
The Old Testament articulates many things as sin that people today embrace as normative including everything from eating certain foods to premarital sex. Would you deny those things are sins? The Old Testament also endorses many things that today we outlaw such as polygamy. So should people of faith live by the Old Testament or not? Finally, the New Testament (which is the basis for Christianity) does not condemn gay and lesbian unions at all. If the NT does not identify homosexuality as a sin why should Christians find it objectionable? If Christians today are being guided by the OT why do they reject things like polygamy and embrace lifestyle choices the OT specifically condemns such as fornication?
If "biblical scholars" of any time period believed that blacks are morally inferior to whites and somehow indicate that that comes from the Bible they are wrong. The Bible states no such thing. That's their own mistake/prejudice.
And Bay, I think you are confusing Mosaic Law w/Moral Law. Moral Law we should try to follow/keep...but Mosaic Law was to "set Israel apart."
Avoiding certain foods (and clothing w/diff materials as someone stated in this thread) were part of Mosaic Law...premarital sex would be in the Moral Law arena.
As far as I know Polygamy was never "approved" as a way of life, but people did engage in it.
And yes, homosexuality is referred to as sinful in the NT as well as the OT but Bay, even if homosexuality wasn't a sin, anyone that has told a lie has sinned and that puts them in need of a Savior anyway. If you read the Bible you will see it states that we all need a Savior. Everyone.