...So at what point, in your mind, did slavery become immoral?
Give us the year, maybe even the month, day and hour that it became so.
When did or does slavery become immoral?
This didn't seem to get answered. And of course the answer is "It depends".
First, one has to decide if there are objectively immoral things and how humans collectively know those or how individual humans know them.
Then you have the problem of what slavery means. There is a long history of different kinds of slavery: debt slavery, chattel slavery, warrior slavery, religious slavery, serfdom, prisoners of war, political enslavement, etc.
Then there is the time and place issue. If the immorality of slavery is not innate to humans or universally taught, then things get relative. There were ancient individuals who saw slavery as immoral and for them slavery become immoral when they had that revelation. When enough people or a strong ruler felt that way, then in that place It might have become immoral.
Then you have the question whether banning slavery of some or all types mean you think it is immoral?
In 1772 England ended slavery in England
In 1807 the UK abolished slave trading
In 1815 the Congress of Vienna declares its opposition to Slavery
In 1949 Slavery abolished in Kuwait
In 1926 the League of Nations proposed a Convention to Suppress the slave trade and slavery. From 1953 - 2008 countries around the world were ratifying that convention.
So to have your answer: It depends. Unless you can show that there is an objective, outside of humanity morality that humans have always had ready access to.
Oh, BTW, are those ants that enslave guilty of immoral acts?
