A couple of a house as an investment is already a lot, and way more than the average person can afford. If you go from a leftist perspective, the fact that they make money without workings sucks. These people who own a couple of house for investment are also the one complaining about “public retirement system is too expensive, so we should cut-down retirement benefit for everyone”

More seriously, I understand that you want to play by the rule in today’s capitalist world. The problem is that in many places the rule are skewed. In some countries income from rent are less taxed than income from work, and the power-balance between tenant and landlord is favouring the landlord (and people see implementing stuff like rent-control and shorter notice for tenant as leftists policies). While it’s fun to say eat the rich including the landlord, you need to build a reasonable political program if you want to stand a chance.

Another big issue, is the lack of affordable rental properties managed by the government/municipality. It’s basically massively promoting either homelessness or bad housing