Most classifications I have seen classify a "mom and pop" landlord as someone who owns 10 or less units in their name (meaning not an LLC).

This is really about aggregate effects. One of these mom and pop investors doesn't have much of an effect on the market. But a couple thousand of them in a mid-sized city each trying buy up a couple houses or condos to rent out or put on AirBnB artificially increases demand, and thus housing prices increaae. And that increased cost to purchase means that's rents are going to go up as a result. Liberals absolutely hate to acknowledge that and will get real fucking pissy when you point out that their little AirBnB side hustle is hurting other people, and they don't think anything should be done about it. I always use the analogy that just because Hitler did the Holocaust wouldn't make it OK for you to go out and murder a single person. They don't like that analogy for whatever reason lol.