The just-in-time supply chains that keep the lights on and food and other goods in the stores would fall apart within a couple of weeks.
Medieval starvation was local. Areas were largely self-sufficient in the bare essentials - except in bad years, which happened regularly enough to keep a lid on population growth, but not so regularly they caused widespread depopulation.
Trade was mostly for useful extras.
That's very much not true today. Everything is specialised and interdependent, and not even farming areas are truly self-sufficient.
This was - and possibly still is - the biggest risk from a pandemic. It's hard to calculate the exact tipping point, but when you have a certain percentage of the population unable to work for a couple of weeks or so, essential systems start breaking down.
If 50% of Canadians died next week, you think what, Canada would cease to exist?
It’s possible. Canada’s nearly broken up* in recent memory over regional differences. 50% of a population dying is a massively destabilizing event that could undo even a comparatively wealthy nation.
* or at least its second largest province narrowly decided to stay in Confederation.
Eventually, some black swan event will happen and we'll have a systems collapse it will be very hard to recover from - because so little of the population will have baseline skills. Thankfully this pandemic wasn't it, but it doesn't seem to have woke up TPTB to the problem.
However i agree with you and i think even the US govt agrees with you. Thats the reason farming subsidies exist