Sorry, but my imagination is clearly not robust enough to even begin to steelman a policy that puts children into debt over near zero-cost food at school, often publicly humiliating the child at the same time, without just sounding like a cruel cartoon villain.
I don't believe any of this, but I'll try. Please note that the below is not my personal belief, just an attempt to understand the "other side":
The attempt to steelman the policy probably comes down to encouraging personal responsibility (the libertarian way). Forgiving debts without consequence promote a culture of non-payment, undermining the sustainability of school meal programs.
The steelmanned version of why lunches require payment is likely down to sustainability of the program in general (ie: school budgets are already stretched to the limit, so parent contributions are necessary).
Now, this could obviously be solved by just budgeting for the entire thing to be included in the overall taxes of the state, but then you've got to surpass the hurdle of tax raises being insanely difficult in the states.
Honestly, this exercise kind of makes me see (yet again) how broken the whole USAmerican system is. "I've got mine and I don't want to give any more away for something I don't need"
