I wonder how many UBI proponents here would be willing to adopt your immigration rules, which go a long way toward making your system work as well as it does.
I'm not exactly sure which rules you are referring to, but if you are alluding to Australia and New Zealand being difficult to emigrate to, I would just point out their respective population growth rates relative to the US (this growth is not due to natural increase - it is immigration that is driving it).
I am referring to the points system and income requirements, which give priority to people who are young, healthy, well educated, in demand, and/or wealthy. This ensures that most who are approved will provide substantial funding into the system before needing to draw from the system. As a result, the immigration-driven population growth you point to actually helps support the system.
https://www.google.co.nz/publicdata/explore?ds=d5bncppjof8f9...