Your argument would be valid in 1950 (or 1650) but it does not apply for 2050. This whole discussion is initiated by the fact that due to changing circumstances, many adults
MUST be "net consumers" in your terms, that's unavoidable, and the only question is how do we handle it ?
In the coming decades, we're facing millions and millions of people for whom the market price of their labor will be lower than the market price of their bare sustenance. We're not there yet, and especially not worldwide, but that's where the trends are pointing so we're discussing it to have a perspective of what needs to be done in the future. There's no "checks and balances" possible - they will be net consumers if they are alive.
Already there are massive industries (e.g. garment and footwear manufacturing) which are not automated only because for now e.g. offshore sweatshop labor for handful of rice a day is cheaper than doing it with robots - but it's changing as automation is becoming cheaper over time.
So that is the big question, what will we do with the growing number people for whom the society has no economical need, who must be net consumers - and there really are only two options, either the society transfers resources so that they can live a reasonable life, or it does not, and they do not live a reasonable life.