I'm not even going to unpack all the bullshit in the 1776 Commission because it's bullshit turtles all the way down. But I will stress that anybody who tells you that everyone at the time thought slavery was this perfectly acceptable thing with no downside is full of crap.
Because first up it cannot be stressed enough the enslaved had some fucking opinions on the subject. But also so did those making the laws. Any law about the treatment of slaves was done with the purpose of protecting the slave owners.
They knew. They knew they were doing something which gave human beings ample reason to rise up and kill them if they found a way to organize and make it happen. You don't do that if you mistake slavery for a vacation outing.
Laws were organized to prevent the enslaved from organizing. Protestant colonies like early America did this by splitting up tribes, assuming the enslaved wouldn't want to form alliances with those who weren't of their group.
Catholic colonies like those owned by France and Spain did it by keeping tribes together, assuming they would rather bond amongst themselves and not make outside alliances. (Note: tribes, not families. Splitting up families was universal.)
There's much more but even here you can see it: They knew these were intelligent people who could make plans, organize, and rebel. You don't fear an organized uprising if you don't believe they have the intellectual capability to make one happen.
Yes there was a lot of justification (usually religious) about how they were lesser humans who needed to be saved from themselves, but there was never the assumption that these were kindly treated people who had no reason to complain. That is horse shit.
And if you want more on proof of that subject feel free to check out this thread I did awhile ago about none other than Georgie Boy our first president and how he treated the enslaved around him.