People automatically equate taxation with fines and coercion, but they're separate concepts. The best example is the income tax. If we slap taxes on things we don't want people to do, then why do we literally tax work, a thing we want almost everyone to do?

So taxes aren't fines or fees, and they don't force you to stop doing something you want to do or do something you don't want to. People still buy groceries despite sales taxes (which, again, we want people to buy stuff).

Thus, the argument that a vacancy tax compels rental property owners to rent their places falls. I'm not compelled by income tax to be unemployed, nor am I compelled by sales taxes to purchase no goods, nor are owners compelled to rent their places.