You are looking at ethics and morality from an individualistic perspective, not a systemic perspective. People opposed to landlords are more concerned with the latter. This is an insignificant edge case needed to construct a situation where the individual and social ethics diverge and has little relevance to policy decisions.

I wouldn't say either is entirely ethical, but the second example is way more ethical than the first. If you buy a house to rent, it doesn't really matter where the house is, you're still preventing a family from having a stable home and taking it off the market for your own greed. With the second, at least you're building housing.