Slaves can handle horses too. My point is slave owners will be reluctant to part with their property just as they were in the South, and fought a civil war to keep their slaves.
But the South was the only place slavery ended so violently, everyplace else it ended organically. If there was no Civil War, it's very likely slavery would have died out on its own accord, just like it did everywhere else.
Slaves are a form of wealth and it is hard to convince people to give up their wealth.
So are trucks, they just require less maintenance than slaves. Making them an even better form of wealth.
Some forms of slavery will continue for example, slavery is an effective way to punish criminals, and I think there will still be crime as technology advances, prisons cost money, feeding and housing prisoners cost money, the Roman government would just rather sell its prisoners as slaves and that way they can pay for their crimes.
And here in the Western world at least, the idea of convict labor has fallen by the wayside, and quite quickly.
Murderers probably get sent to the arena, or they are simply executed in public. Probably crucifixion would continue, another form of execution is feeding them to beasts. The point is to deter crime by making executions public. Human collateral could also be used for personal loans. A Roman citizen can take out a college loan, and if he can get a job and pay it Off, fine, otherwise he may become an indentured servant. The prior career rolls would include a chance if being sold into slavery as a possible mishap. The price of slaves would go down as the demand for slaves decreased., but it would still exist to some degree because of social inertia.
So how is it that today we've managed to evolve out of that?
We don't torture criminals to death any longer. Closest we have to blood sport today in MMA fighting and cock fights in the alley. Even car racing is evolved based on safety more than anything else.
Some societies still have bloody, public executions. But we also know the global opinion of that and no doubt there's pressures on those societies to perhaps revisit those practices.
Technology developed slowly in the early history. As they say, up until the first locomotive, horseback was the sole mechanism for land travel to the point that George Washington moved his army the same way Julius Caesar did. Or that the Space Shuttle design was influenced by the size of a horse. But that about 250 years ago. Since then, it has taken off.
With that, populace mobility has exploded. Now, barring state controls, it's easy for someone to leave a place they don't like to try to find a place they do like.
With technology comes communication, with communication comes evolution. Look what's happening today because of the modern communication networks. It's hard to imagine a high tech society not going through a similar evolutionary phase and even more difficult to think that they might go "Yea, it was better in the past so we'll go back to the slaves, gladiator games, and nailing people to things".
I just look at all of the different things that can fracture a locked down society. Even today we see the effort it takes to keep a society closed off.
I think it was inevitable that those Roman institutions were left behind, and that even a future Rome, while perhaps still semi-glamorizing it through rearward looking, rose colored glasses, would have left them behind as well.