So we're comparing "property taxes", which are on the value of the empty land + any improvements, against "land value taxes", which are just on the value of the empty land.
_naply asserted that one reason to favor LVT over property taxes is that property taxes discourage people from building on it; and gave "speculators" as an example. We didn't flesh out exactly what that meant, but I took it to mean people who bought some area of land which right now is close to worthless, in the hopes that in the future might be worth a lot more.
(One alleged example of this is in Detroit city proper: allegedly, people bought broken-down old houses near the city center for a song, but didn't actually repair the property; they were just hoping that in a couple of decades things might turn around -- based on the efforts of other people to make Detroit better, naturally -- at which point they could sell the land at a massive profit without having to invest anything themselves.)
At any rate, the argument is that such speculators would otherwise build something useful there, but had decided not to because then they'd be paying more property taxes.
I don't buy it: As long as whatever they built brought in more money than the property taxes, there's more money to be had from building than from not building. The hypothetical speculators in Detroit could certainly build a single-family dwelling and rent it out for 30 years, and extra property taxes would almost certainly be outweighed by the additional rental income.
But the value of speculation is that it's low-cost and low-effort, and low-income rental is distinctly neither. Why bother dealing with contractors and repairs and tenants and whatever before selling it for 20x what you bought it for, when you can just do absolutely nothing and get almost the same return?