So.. sell or lower your rent? If you’re saying that what you’d do otherwise is sit on a bunch of empty housing hoping for a market correction, it seems like you’re just violently agreeing that such a tax would have a net effect of reducing vacant housing by disincentivizing overly speculative development and holding.
In other words, maybe if you’re not holding the bag (that is, your bad investment), that just means everyone else is instead.
Say you're already charging the lowest rent that makes economic sense (i.e. at cost) and you still can't get tenants? What then? It's not like anyone is going to want to buy the place from you under those conditions. Your best bet would probably be to tear the place down in hopes that without an actual inhabitable residence on the property it will no longer qualify as vacant for tax purposes. Perhaps even get the land rezoned from residential to commercial. This certainly won't do anything to improve the availability of housing when demand eventually picks back up, but then that's an entirely predictable outcome of attacking "speculation".
In other words, maybe if you’re not holding the bag (that is, your bad investment), that just means everyone else is instead.