Vilifying private landlords is helpful in advocating for public housing and denouncing Rentier Capitalism. Rather than seeking to live off the wages of others, people are better served by earning a wage themselves.
The shortage you mention, do you think it would exist or exist in as significant a degree if landlords were not buying properties they have no intention of occupying?
Under capitalism there's an incentive to manufacture a shortage to drive prices up. That's why Vienna has such a higher quality of life than anywhere in the US: robust public housing which does not have such a detrimental incentive.
