Buy from a speculator and you get to enter the market at a price of their choice.
Vacant land is land that somebody could have built a home or a restaurant or a storefront or an apartment complex on, except it's being hoarded by speculators, who often refuse to sell at a loss.
In order to build a home / restaurant / storefront on that land, you first have to buy it. Buy it from whom? Ban speculators, and now you have to buy that land from the original owner, who is obligated to hold on to it even though he may want to use his capital for something else.
> refuse to sell at a loss
Speculators who won't sell at a cash loss are a real problem, but it's a problem that can easily solve itself. As the land value fluctuates up and down, the speculators' investment also goes up and down, whether he sells at that price or not. Carrying a piece of land on your books at a loss inflicts economic damage on the speculator.
In a free market, bad investors getting wiped out is just as important as useful ones getting rewarded.
Simply make the "default setting" to allow building things everywhere, and stupid speculators will go out of business more or less instantly. Useful ones will continue to quite literally make money for themselves and society.
> Buy it from whom? ... now you have to buy that land from the original owner, who is obligated to hold on to it even though he may want to use his capital for something else.
There's no obligation to "Own" land, if you want to put your capital elsewhere then either use your existing land as collateral for a loan or otherwise sell it. Technically everyone is actually leasing land from a government, it's not a commodity and it has a finite supply, so unlike corn or even housing, what is a speculator even speculating on?
I also want to be clear I think it would be very silly to ban speculators, the act of speculation is something that we all do when we own literally anything, but speculating on limited finite ground space that no one actually owns doesn't make any logical sense. Just properly tax speculation into a space that is unprofitable to hoard.
Vacant land is land that somebody could have built a home or a restaurant or a storefront or an apartment complex on, except it's being hoarded by speculators, who often refuse to sell at a loss.