Advocates of the vacancy tax imply that their goal is to eliminate vacancies thus freeing up more housing. If our goal is, instead, to maximize tax revenue in order to build permanently-affordable housing then that is a much different (and better!) conversation. That's a long-term good.
But if that's our conversation then everybody needs to be prepared for the possible answer to be that the vacancy tax should be negative.
Could be a good idea to use the vacancy tax to build.