> With a basic guarantee many people who are marginally employed would stop working.
So what?
> You'd have two classes of citizens: the workers and those who are effectively parasites off of the workers.
We already have that; the latter class is called "capitalists". With a BIG, the public commons become an equally-owned, dividend-paying asset, which in effect makes everyone at least a very-small-scale capitalist.
> I don't like people being poor but society is just not wealthy for poverty to disappear.
Reducing the necessity of continuous wage labor for those without large personal fortunes increases labor market mobility, opportunities to explore higher-risk, higher-potential return activities, and opportunities for job retraining for better fit to changing markets.
Yes, a cost of that is that some people will opt-out of work without engaging in even potentially socially-useful activities, but this is to an extent self-limiting (the more people do it, no matter the nominal level of the BIG, the less goods and services the BIG will suffice to purchase, so that the more people that opt out, the less attractive opting-out becomes.)
> Part of the issue is that we lack an understanding of poverty and what actually causes people to not be in poverty.
We actually understand poverty quite well, and understand very well that the combination of limited goods and inequality in the distribution of goods cause people to be in poverty. What we don't have is a mechanism that works with human nature to encourage enough production and equal-enough distribution of goods to eliminate poverty, and BIG isn't, itself, intended to be a solution to that. Its mostly a self-regulating partial solution on the distribution side, since, as productivity increases, the sustainable minimum level under the BIG increases as well.