Never thought I'd see the day that a pg essay crosses over with /r/politicalcompassmemes The problem with "discussing ideas" as a framing is that it exists in opposition to something. What is that something? Those whose position favours the status quo would read it in opposition to "not discussing ideas", which is obviously bad. However, to those who find the status quo untenable, the opposite position is "acting on…
Slavery had existed in almost every society throughout history (and beyond, no doubt). The word slave comes from the Slavs of eastern Europe, who were captured and enslaved by the Turks and Barbary pirates.
Then there was a unique event: Protestant (many non-conformist) groups in the wealthiest democratic country (Britain), decided to campaign on a fundamental principle of Enlightenment and Christian human rights. It was a vivid debate of ideals and economic practicalities, conducted in the Mother of Parliaments, and on the streets outside.
Britain was a major beneficiary of slavery in the American colonies and the Caribbean. It would have renounced the trade, and the practice, in the late 18th century, but the military and economic imperatives of the French Revolution, American Revolution and Napoleonic Wars intervened. So the British slave trade was not abolished until 1807, and the practice of slavery itself in 1833.
Britain also had the largest navy in the world at that time. It not just passed laws for its empire, but also actively blockaded Atlantic ports and intercepted the slave trade from Africa to Spanish and Portuguese colonies (both Catholic, not a coincidence). It was later joined by the northern Yankee navy in the Atlantic and on the Barbary coast of N.Africa. Slavery was abolished in the US and Russia (serfdom) about the same time in the 1860s, but it lingered in Cuba and Brazil toward the end of the 19th century.
T.E.Lawrence commented on the slavery he found in Saudi Arabia during World War 1 (1916) [Seven Pillars of Wisdom]. The practice of legal slavery continued into the 1970s in the Gulf States, and the indentured servitude practiced there today is little different (long working hours in difficult conditions, physical isolation, confiscation of passports, non-payment of wages, no rights in the legal system, sexual abuse of women, etc.). The fact that these countries are undemocratic unenlightened Arabs is also not a coincidence (Arabs seem to have an extra cultural level of racist arrogance, over and above the intolerance of other Muslims in non-Arab countries, such as, say, Iran or Indonesia).