Things never change, until they do. Think about the extreme case, where a $10,000 machine can do any job that humans currently do, better than they do, 24 hours a day. Would the entire world find new jobs, everyone doing things that no one up until 2013 had ever done before, things that machines are still not capable of, things that are valuable to the economy? I doubt it.
At some point, the machines will win, and everyone that doesn't have the means to own machines and/or integrate them into their body is going to have a really hard time of things. Just how soon is debatable, but the way things are going I won't be surprised to see it in my lifetime.
When you assume the outcome, of course it's inevitable.
But consider: machines are still dumb. At the end of the day, someone automates the process.
If all work that is necessary for the function of life can be automated, how wonderful! But, consider the dishwasher. It saves time, but is often misused by dirty dishes going in without pre rinse and disposal. So technically the work has been automated, but parts of the work still require manual operation. But now we pay people to pre wash instead of wash.
If we make a better dishwasher that does not require pre-rinse, what happens to your argument? Is your argument that there will now be some other task, maybe loading the dishes?
Consider: washing the dishes across a town employs 1000 people. Pre-washing the rishes employs 300 people. Loading the dishes employs 100 people. The factory creating the dishwasher is automated and employs 10 people. 50 people are involved in designing and marketing the dishwasher.
We have now gone from employing 1000 people to employing 150. Those 850 people are now unemployed and must seek or create new employment. Whether they succeed is irrelevant though, the dishwashing process now needs fewer employees and economic benefit has moved from the employees to the smaller number of people creating the dishwashers.
So your argument doesn't work for a simple reason: automation (by definition) reduces the number of people required to complete a task.
At some point, the machines will win, and everyone that doesn't have the means to own machines and/or integrate them into their body is going to have a really hard time of things. Just how soon is debatable, but the way things are going I won't be surprised to see it in my lifetime.