Landlords individually may not be evil, but the landlording class is opposed to the working class. Like you said landlording is a business and they will try to get as much rent out of you as possible, and in turn the tenant will try and pay as little rent as possible. This is class conflict. Any person, or structure or system your in conflict with over basic necessities like housing you may call evil, if your inclined to the good and evil morality view.

The critique of landlords is that they are a small, wealthy and powerful class extracting wealth from a larger and poorer class while not actually producing anything. They don't produce housing, they just use their capital to buy it and then rent it out. McDonald's may be taking money from the poor but at least they're producing the burgers they sell.