I think I see where you're coming from. If something isn't really necessary for us to do anymore, it becomes a luxury and as such finding it immoral becomes much easier due to us not really suffering without it. I don't lose anything by giving up my slaves, we have machines for that. Right?

In my opinion, that misses a crucial point: Where do innovations come from? What caused the industrial revolution? There's an argument to be made that greater freedoms in the UK after the abolition of the monarchy made the crucial inventions possible - and worthwhile. We can't just say that slavery went out of mode because of the industrial revolution, because that revolution was in turn powered by improvements in public life. People put their life on the line, and they improved their lives - and the lives of countless others.

If it didn't, if we needed to be starved, worked to death, so that society could continue, our social structures and beliefs would shift until those things became commonplace, accepted, and rationalized.

History doesn't bear this out. Societies where this begins to happen inevitably crumble long before this happens, or get abandoned, or changed. See the french revolution. See the potato famine in Ireland. People won't take shit lying down.

Rather than society being shaped by progress, it is society that is shaping progress - we improve upon things we consider important. If animals don't have to die anymore because of lab-grown meat, that's because we wanted to invent that alternative! Because of societal pressure to stop killing animals. The same is true of all other moral changes. There's always a group that has been advocating it beforehand, and they work to convice other people that their view has merit, and eventually people come around.