Your previously-4-to-16-year-old kid was also eligible for, you know, school, and that wasn't paid out for by his own tax dollars either.
It's not the source of the tax dollars, it's the purpose behind those tax dollars. Every child
needs an education and society provides. An 18 year old living at home in suburbia
does not need food stamps. An 18 year old not living at home, unemployed, may very well
need food stamps to get by. An 18 year old not living at home struggling to feed oneself (and perhaps their offspring) most certainly does not
need cable TV. What they in fact need is to cut the cable. Thus my argument for strict condition-based eligibility requirements.
Direct benefit social programs (food stamps and welfare, not schools and libraries) are supposed to serve a defined purpose - help those in genuine need (on a temporary basis if able-bodied). They should not be programs that can be merely gamed by the clever. I think what is tripping people up is the mixing together of various tax laws (which we all jump hoops through to minimize our tax burden) and social welfare programs. They may end up at the same end result but they are hardly the same thing.