They didn't know that it would probably become an airbnb, but the likelihood of such a place becoming one or being bought by somebody else wanting to charge higher rents isn't exactly low either.

The whole "market rates" thing is used by corporate landlords to increase prices, and controlling available properties - including by leaving vacancies - is one way that do that. By the same token, charging below "market rates" could also help of enough did it, especially if the places are decent and money re-invested in proper upkeep. Many/most though are not even investing in proper maintenance/repairs while charging over an above the cost of entire mortgages, which IMO is just greedy bullshit

I mean I guess I could have left it empty while I myself rented from someone? I don’t see how that’d make me a better person though.

I’m not really buying your argument. You’re not making any real argument of how I hurt anyone or even caused a net negative on society. You’re speculating that because I didn’t hand the house to someone “who needed it”, that I somehow did wrong. I didn’t price gouge. I didn’t raise the rent. I repair things in a timely manner. The renter pays less than they would if they bought the house, aren’t responsible for anything major, and can leave at just about anytime. Seems like a net positive in my book? Sure, they paid me… but am I supposed to give it away for free? Selling it probably would have landed me more money. Are you pitching a world where everyone has to lock in to a 30 year loan and be stuck there? Or is this an argument where housing should be free or something? (Sure, whatever… but that’s a different topic)

You aren't saving people money by taking rental payments, you aren't a hero for potentially stopping someone from using the property as an airbnb, you are a landlord.

I don’t think I’m a hero. I do think I’m saving them money. They could have foregone a rental and bought a house. They chose not to to save money for a business.