I think stricter government controls over not allowing buildings fall apart is a better solution than cranking up taxes, or trying to take away the properties from the owners.
I rent out a small apartment I used to live in. Rent is below market rates cuz the little old lady is the best tenant I could hope to find. Raise taxes on that place because you fantasize that everyone is a slumlord, then I have to raise rents. Apply rent controls in addition, and that lady gets the boot cuz I sell it.
I don’t think your solutions are actual real-world solutions. I think they’re solutions to a perceived problem (evil slumlords) rather than what is happening in the real world.
So because you're doing someone a solid, that means slumlords and exploitive landlords aren't a real problem? Come on man.