Simplified analysis, goal is situation C. Let's say my monthly welfare income is $1000.
A. I start earning $200. My welfare decreases by $200. Why don't I just stay on welfare?
B. I start earning $200. My welfare decreases by $300. I've lost $100, a penalty for working.
C. I start earning $200. My welfare decreases by $100. I now have an incentive to work. Over time, this leads to a future situation where I gradually earn much more than I could ever with welfare.
Also consider: What if I find $1000 sufficient to live on? What about $1100?
I start earning $200. My welfare decreases by $200. My expenses increase by $100 (transportation to/from work, childcare while at work, clothes specifically for work, etc).
Once you realize that work usually has more costs than just time A and B become the same.
For now, we're talking about unskilled and low-skilled jobs going away permanently, and there is an element of moral panic about uneducated, supposedly low-value-producing people getting leisure and government support.
Just wait until it happens to a middle-class or upper-middle-class group. THEN is will be all kinds of innovative to offer lifelong government assistance in the form of mincome or other such program.
And if you are worried about government spending and efficiency, wouldn't you rather see the TSA payroll supporting twice or three times as many people in a mincome program? It's better to be honest about a lack of productive jobs.
These things don't happen overnight--there will be many years as the class of jobs that you're talking about becomes slowly less well-regarded, until when they disappear no one will care.