There's always some risk that infrastructure will catastrophically fail, and in general I think a month-long self-sufficiency stock is a perfectly reasonable thing to have. (I have one myself, although primarily because I live in an earthquake zone.)

But when people are reacting to the coronavirus, the implicit question isn't what preparations are good to have for general worst case scenarios; it's which preparations you're likely to need, which ones you can no longer afford to be without. As many a doomsday prepper will attest, there's always one more contingency you could plan for, but telling people to start with extreme measures makes it less likely they'll plan at all.