> The problems would be that the real implementation of basic income will never be as simple as proposed. We would start out by saying every adult will get a fixed amount. Then the question comes out about people with disabilities needing extra money for their care. So we carve out an exception.
Or, more likely, we don't include disability programs (which are not purely or primarily means-tested programs) as among the primarily-means-tested programs that are replaced by UBI in the first place. To the extent that improvements are needed in disability programs, they come from elsewhere.
(OTOH, part of the problem creating incentive for disability fraud is secondary testing in primarily means-tested benefit programs, which leaves lots of gaps in basic poverty support.)
> What about parents who squander the money and the detrimental effects on their kids. Do we let the kids starve?
We deal with child neglect through child welfare systems, not social benefit systems.
> What about kids in foster care?
What about them?
> What if parents have lots of kids?
Then...they have lots of kids.
> Should kids also get a basic income?
Pretty obviously, yes, kids should get basic income (if nothing else, most of the primarily means-tested social benefit programs -- both welfare and EITC -- in the country are support programs for parents with dependent children that are strongly scaled by the number of dependent children, so if you want a system that does at least as good for current targets of benefits while removing the adverse effects, the obvious methods is that kids should be included as beneficiaries. There are a few programs that are not targeting such families -- e.g., General Assistance programs, but they are small both in their per-beneficiary benefits and their aggregate costs as a share of overall social welfare spending.)
The most sensible way to do a UBI is probably "all citizens and legal permanent residents".
> As we add more and more exceptions there are more opportunities for abuse of the system.
The whole point of the "U" in UBI is that you don't add exceptions. You define a broad universe of recipients with as few qualifications as you can sensibly make, and everyone within that universe gets the same benefit.