In the US alone, there are over 17 million vacant residential properties. Average un-occupancy rates for urban areas run 10%. That is more than plenty to house every homeless and very poor person.
There ought to be massive taxes on urban vacation, vacant housing, and entirely airbnb properties to encourage utilization by those who require housing rather than being hoarded/exploited by those who use them for recreational/investment purposes.
It’s a notoriously silly take.
Most vacant homes covered by that statistic are either 1) uninhabitable shells in low-demand rust-belt metros; or 2) houses that are for sale or between tenants. A small percentage of them are second homes. And while you could of course raise taxes on those homes (a policy I’d probably support in some form), it’s unlikely that it’d have much of an impact on the overall problem.