Yes they are horrible and yes they are exploiting people. It's not a service, they are exploiting the capped supply of a basic need.
The argument about "if nobody rents out" is just wrong. Are they going to knock the place down if they don't rent? Yes there is a need for rentals but this should be within a world where we have land value tax so the bulk of the gain is passed onto the state to reduce labour taxes, reduce land costs and improve living standards.
These guys are adding nothing, they are taking labour.
The cost of a home is not the cost of the bricks it's the cost of the land in the main areas with employment prospects.
The USA was originally a land of opportunity. Why? Because you could get hold of land cheap. You were no longer constrained to near-serfdom by total land enclosure in Europe. Now here we are back to square one with the rentiers creaming off labour and books on how to join them.