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.
Why it's possible to highlight the negative effects of capitalism in general, I feel like that's a "boil the ocean" problem.
The root of the housing issue is supply. It doesn't matter who owns the accommodation - there's a shortage of it - and that's driving prices up.
I more useful strategy IMO is to look at policies that would encourage all levels (private and govt) to develop more housing and increase the supply.