That presumes the outdated notion of perfectly rational consumers. Economists have discovered that consumers aren't rational anyway, but in the case of a pandemic the likes of which western consumers have never seen, I can assure you that consumers are anxious. Some consumers are even panic buying, and their purchasing habits are consequently even more irrational than usual. Even assuming you and I both manage to stay rational, other customers hoarding will affect our respective purchasing powers. (Tbh I'm not immune to group psychology which means panic buying.)

When a hoarder has a 5 years stockpile of TP and others have none, that's obviously inefficiently allocated in a time of need. Given that we've seen that the is market unable to handle panic buying and hoarding in (perceived) emergencies, strict allocation of certain necessities during an emergency really does seem like the easiest way to equitably handle the situation. More creative solutions may exist, like volume purchase surcharges, as seen in a Danish store [1], but by and large, "limit 1 per customer" seems entirely reasonable. (For whatever value of 1 is appropriate for a particular product.)

[1] https://nypost.com/2020/03/21/danish-store-instills-pricing-...