People stopped being farmers because their manual labor got automated. They could still use their brain and other hard to automate stuff like their hands and eyes to make money, though. Nowadays, we're starting to automate not just hands and eyes, but increasingly the brain too. There will be just one "skill" left and that is being human. This skill is rather important in entertainment, arts, horeca, health care and medical stuff. Do you see your average factory worker or truck driver work in these sectors? I don't. There will NOT be more than enough to be done that requires humans and we're already starting to see that today. This will happen to loads of people that do not posess any skill that hasn't been automated or are not quick or flexible enough to learn new skills. These "useless people" will not "find other stuff to do". We will therefore need to find alternative means to keep them busy. Basic income sounds like quite a nice - if not the only - solution. We should, however, make haste, because there's only one alternative to basic income and that's an unescapable oligarchy, where all production and transport capacity is owned by a handful of people. That's something that should be prevented anyway so basic income should probably be set up in such a way that the people are effectively the shareholders of the planet, which is in fact really not that difficult to get right. The alternative is that the vast majority of our posterity will be born into effective slavery.
And it would be quite ridiculously sad if that were to happen because you believe that "people will find other stuff to do because they did so in the past". We already today have many people that are incapable of any contribution. As we raise the bar, this group will grow and it really isn't that difficult to understand that there are limits to this, simply because there are limits to human (brain) capacity.