I've no issue with people renting out, or even people who inherit a home or anything like that, and renting it out. Where I have a problem is people who use words like "portfolio" or investors who buy or build entire blocks of shoebox sized flats to rent out. People like that deserve to have their properties burned to the ground, but sadly the small landlords will likely go with them.
I see them everywhere here in London, they're going up like lego buildings. We've looked at a few and they're absolute insults towards renters, I can imagine an accountant and an architect looking at a reasonable sized lounge and goingv"if you put a partition here you can create an extra room and increase the price by 20%". Those people don't belong in our society.
Where your mistaken is the problem is not these people.
The problem is the lack of alternatives. It's not the role of the private market to provide housing for all incomes.
If someone wants to build and rent 5 million a year apartments that are the size of a bath tub why not?