1) A vibrant middle class is an aberration of history. I don't think we can look to history and find meaningful examples of what exponentially increasing technology will do to our current social structures.
2) Our society determines what basic income is. Just like we determine our laws.
3) Living in a society that respects property rights has its costs. Almost the only difference between the relatively peaceful western world and places like the unrest in the middle east is that the vast majority of our population has a lot of opportunities. You take those away and we will have the same unrest here.
I tend to agree with Thomas Paine, who believed that all citizens have a natural inheritance created by the introduction of the system of landed property. So in return for society recognizing property rights those property holders owe society some of its proceeds. He explicitly stated this should not be considered charity.
4) He never said he thought there would only be positive results. He did say he thinks it would be a good idea, but plenty of good ideas still have consequences. And he was openly asking for other opinions while merely offering his own; there is no need to jump down his throat.
5) No one is saying people would be paid not to work. All people would just be told "you don't have to work to meet your basic needs." Once that burden is removed, people would still be free to work to better their lives further. Very few people would just sit around all day doing nothing, and those that do really would be the ones we want removed from the workforce anyway.