Is it the threat to higher skill jobs? Because it seems to me quite normal: since it began automation has taken over progressively more skilled tasks, starting with the least skilled labour.
Is it the threat of higher education/skill requirements for jobs? Automation, by taking over the lowest skill jobs, both creates higher skill jobs overseeing and creating the machinery and pushes the labour pool to a higher average education/skill level. Is there a critical point we're reaching? Will university education become required?
Is it purely about numbers? The aforementioned process of automating low skill jobs while creating higher skill jobs includes within it a general reduction of jobs (leaving aside the creation of new job markets like entertainment or information workers). The low skill jobs are the most numerous and the newly created jobs are much fewer. Why have we been able to keep people employed despite automating away shovelers, weavers, and almost all other manual labour? We even have a much much larger population since the industrial revolution began, what process created jobs for everyone?
So what is full automation then? Don't all machines and devices need maintenance or replacement?
Retail is I think an easy target for automation because people are trained not to steal, and lots of stores have minimal staff and put more and more "work" onto the purchaser ("Ye Olde Shoppes" had all goods behind the counter and the clerk would fulfill your order, less modern shops had floor staff to assist customers, current shops have the customer fill a basket and the clerk rings up the price, future shops have no staff at all). Some might characterize this as the slow collapse of the retail bubble where people buy from warehouses or manufacturers directly.
But doesn't history demonstrate that humans opt to do different tasks than the ones automated by machines? Or are you saying that in the mid-near future AI & machines will be better at all economic production than humans? I certainly agree such a point will come, but the things humans value change with their needs- if shelter/food/entertainment are all mass produced and easily/cheaply available, humans will put value on other things/activities. For example, hobbies are making a comeback and there is a rising market for handmade items despite being more expensive than the equivalent mass produced low quality item. Humans are valuing the construction and quality and "craft" (art) of an item in tandem to its functionality.
I agree that in general people "work" because of an inherent drive, because it brings happiness, rather than the economic incentive. The economic incentive forces people into jobs they hate and prevents them from pursuing their actual interests because they need money.
What will become of that drive when every avenue or outlet for it is fulfilled better, faster, cheaper by automatons?