It is a service that comes with plenty of duties and risks, at least if you want to have a reasonable reputation.
It probably depends on local market. I can imagine that in Silicon Valley, bad landlords can get away with almost anything, because the demand is so strong. Outside such economic hubs, the market situation is much more balanced and getting a good tenant who won't smoke in the house and destroy furniture is not trivial.
A friend of mine rented out a small apartment inherited from his grandma (nothing expensive, a rust-belt city in Eastern Europe that just keeps itself alive) and found out that the tenants turned it into a meth factory, when police came knocking on his door to ask unpleasant questions.
You never felt like an economic parasite. Maybe your tenants were okay financally and you didn't squeeze or kick them out. But some renters do squeeze or kick out poor people. That's where the parasite part comes in.
It's not really that subsistence farming is inefficient, it's just that subsistence farmers (by definition) are not selling food on the market.
This is very hard to understand. Why does this happen? Do you really own your property if you can't sell it? Or do you just have a permit to use it?
The former results in community, and investment and a large number of beneficial economic effects.
The later is simply an economic parasite
Only have to look to the past to see what happened with farming. Substance farming and feudaliam was inefficient and disincentified investment.(why improve land you don't own and someone else reaps the benefits of what you sow?)