When you start instructing landowners what to do with their property, that’s infringing upon property rights especially if failure to do so results in penalizing them.
Your argument states that empty land would be better served if it’s used for other human beings. The same argument if applied to a time scale rather than upon land resources, it is rational to conclude that our planet is better off if people had 1/2 surviving child per person until we hit carrying capacity.
If land owners should be taxed for owning land they don’t use, we should also have a child tax for future exponential growth of a certain set of genes who will monopolize the world’s population by over breeding.
Humans can continue to enjoy baby making(it’s not unlike some human beings enjoy owning vast tracts of land they dont put to use) but left to their own devices and without encouragement, if they are allowed to bear the full cost of raising the fruits of their loins, I think the numbers will go down dramatically.
If goods cost as much as it takes to make them..especially food which is grown at tremendous costs(not just monetary), we will realize that the abundance is a myth and scarcity is our reality.
Re: Your final point..people who own property don’t contribute to suburbs and rural sprawl. It is those who can’t make proper decisions personally and financially who make choices FOR themselves. Things like where to live, what job to do and what to study are easy choices. Inheriting illness, disabilities are choices we didn’t make, but was made by nature for us. We take care of vulnerable people who had no control over their deficiencies because we share as a species DNA with them.
That obligation and duty towards our collective humanity is entirely different than feeling responsible for personal decision making.
Sometimes people make terrible decisions for themselves because they are unable to make best decisions for themselves. In those cases, we have to make decisions for them if we feel responsible for them. These kind of things never end well as history as shown and is best avoided if possible. An example would be the mentally ill. Many refuse to take medications and their circumstances cause them to suffer. Those are tough decisions. But even then there is no need to penalize private property owners.
None of these issues are connected to each other. I doubt if anyone cares about urban sprawl. An easy target is private property owners and that comes from what I can only term as jealousy in simplistic terms.
In today’s world, we have managed to conquer crippling poverty even though there is much work to do. GINI co-eff fueled inequality makes villains out of the property owners. That is a dangerous path to take..once again, as history has shown us.