Firstly it isn’t a myth people have 5 kids, lots of large single parent families exist. Where did I say ‘just for the benefits?’ I didn’t, you put that link in yourself. I even suggested some may choose to have less kids rather than more. The new system would have significant administration costs too, new software, staffing administration etc. Your assumption that crime would fall is just that, pure assumption, you can’t assume crime will fall, it isn’t just committed by the poor. Prices will rise, criminals will want their cut.
Prices increase with change usually, it always generally has when big changes occur and retailers and entrepreneurs want their cut of our money or to claw back losses from lean times, see decimalisation, joining the EU, Brexit, Covid, introduction of the Euro abroad etc, all saw price increases in affected areas, I see no reason why this wouldn’t cause inflationary rises. Immigration would definitely increase, people would want free money, where is the infrastructure, who is going to pay for the additional nurses, doctors, dentists, teachers, schools, housing that we need now, never mind if it happened. Taxes would have to rise to cover the inevitable shortfall imho. I really can not see it working, theories rarely play out how you think as mankind will find a way to feck it up, we always do.
I absolutely agree the system is broke, I’d love an extra £1600 a month, but there are far more needy people than I and you can’t just print money it effects the economy brutally, borrowing has to be paid back, when it isn’t it effects our worldwide financial credit ratings, that determines our interest rate of repayment, look how that dived on brexit.