I'm a renter, and my parents have never owned a house, so I've dealt with landlords all my life. I don't agree with "landlord bad". Are there shitty landlords? Yes. But it's a leap to go from that to "all landlords are bad".
Can you imagine the backlash from the same left-leaning group that goes "landlord bad" if you applied the same logic to a racial or religious group?
Landlords serve an important purpose in the marketplace and any uncontrolled rampant exploitation is a failure of the government and not the entire group of people who sell the service.