Holocaust was so striking to contemporaries, despite genocide being fairly common in history, at least in part because of its technological efficiency.
Technology also allows for more leverage. Hitler need an entire modern nation state with millions of people, semi-autonomous robots may give this power to a group of thousands.
Not really, Genghis and the other khans killed more than Hitler using a fairly simple technique: divide the captives by the number of your soldiers and each soldier is tasked with killing the captives assigned to them.
They usually had around 100k soldiers, armed with bows and knives, and killed tens of millions.
My point is, you don't need technology to achieve bad things and it is the wrong thing we are focusing on when trying to prevent these things. Nukes can already annihilate billions yet here we are, not being annihilated by nukes.
You could program a ethereum smart-contract virus, which hires people to scam money, produce slaughterbots, ship them to a city and strategically hit the soft underbelly aka airports, roads and railways and communication.
If you stack the attack into waves and have the slaughterbot parcels piled into flats by gig workers, you can have a ideology free terror attack that kills millions.
Such ATTAC-CELLs without members, are part of my games lore.
Here is a picture of a standardized factory, made from standardized components, making "slaughterbots" made from standardized components.
PS: The main building block is a sort of hangrenadesized fuel-container, with a fuelcell useable fuel that can be chemically primed to be a explosive. A standardized battery that could be exploded would do too..
Technology also allows for more leverage. Hitler need an entire modern nation state with millions of people, semi-autonomous robots may give this power to a group of thousands.