> We had a moral belief in the equality of the races, rooted in Christianity, long before we had the scientific evidence to support that belief.
Some Christians might have had that belief, but many racist (and, years earlier, slave-owning) Christians believed the opposite to be true, and used the Bible to justify slavery [1]. Jefferson Davis was quite explicit about it [2]:
> [Slavery] was established by decree of Almighty God...it is sanctioned in the Bible, in both Testaments, from Genesis to Revelation...it has existed in all ages, has been found among the people of the highest civilization, and in nations of the highest proficiency in the arts.
When I say "based on evidence" I mean that bills must have some basis that everyone can agree on. People may not agree with the conclusions, but there is a firm basis there nonetheless.
It doesn't take a lot of imagination to consider the consequences of religiously based laws. Imagine you're a Christian in a small town, and for whatever reason, your town becomes a popular place for immigrants/refugees from the Middle East to settle, and all of a sudden your town has a slight Muslim majority. Would it be ok for them to vote to require all women in the town to wear hijabs in public because they believe God demands it? To such a proposal, you might say "that's absurd! God doesn't want us to wear hijabs!" There's no way to settle the argument, because there's no evidence for the claim one way or the other.
That's the problem with laws based on religion, and that's why our constitution protects against them.
[1] https://time.com/5171819/christianity-slavery-book-excerpt/
[2] https://en.wikipedia.org/wiki/Christian_views_on_slavery#Opp...