On one hand, technological improvement has deprecated thousands of farm workers over hundreds of years, but you're making the argument that it's only happening now because some factory workers lost their jobs. People have been losing their jobs for a long time. Blacksmiths are very rare now a days, but were very common only a short while ago.
The second argument you make is that people will have to work multiple menial jobs to barely get by, yet you also state that menial jobs like factory work are going to be replaced by machines. If the jobs are replaced, nobody is going to be doing multiple menial jobs as those jobs won't exist.
There's only two options in such a doomsday scenario where all work is done by machines. Either humans will be given some kind of basic income, or the rich will get an army of machines and wipe out all the people they don't want. Or a combination of the two, such as humans given a basic income until the rich get tired of it and then build an army of machines to wipe everyone out.