They also play games where they refuse to lower rents even when they're going empty because it will lower the resale value of the property. There's lots of economic games you can play when you own a large percentage of the rental property in an area. The logic of "landlords provide housing" is a myth, but it's especially true here when the primary purpose of owning the property for these firms is speculation and collecting market rate rents is secondary to that.

exactly. Not everyone wants to own their own home. This actual increases rental supply.

if you want more housing, build more houses.

Changing % ownership of houses between individuals/companies via government mandates does not actually build more houses.

Is increasing the rental housing stock an intrinsically good thing if every unit of housing available for rent means one less unit of housing available for sale?

Here on HN we're all quick to lament the end of real ownership in the sense of media like books and music, at the mercy of an exploitative corporate practice that is not coincidentally called rent-seeking. So why should we all be happy to be literal rentiers to the landed gentry?

To drive down the price of homes, because owning is better than renting. Rentals will still exist, I promise.