Renting allows those without the needed capital to access a resource.

Backing out from that, one should question why shelter is a resource that someone cannot access on a minimum wage salary.

So, fundamentally, landlording isn’t inherently evil, but it’s presentation in the system is inherently corrupting. As in, at any moment that someone retains an excess of shelter they do not need, and instead rent it out, they are constraining the market for their own gain, at the detriment of others who in need shelter.

Next consider degrees of influence: large corporations buy up tons of units and exert inordinate power on the system. They systemically unbalance the purchasing ability of normal folk, due to process or sheer wealth. Fine, that’s the high water of corruption. From there it’s only shades of difference down to the mom and pop landlord. It’s up to you to decide where they land on the scale.