That's a simplistic and skewed point of view. Have you read the Healthy Homes standards?
If there is a shortage of rental housing, people will be much more likely to bunk up together. And there does seem to be a shortage atm, though perhaps mainly for those the private sector is not at all interested in offering a tenancy to.
If a rental does not meet all the current and coming soon standards landlords are in for huge fines. It does not mean the property is dangerous, or a slum. It might mean the insulation met the standard 3 years ago but no longer does. But might well mean the insulation does not get topped up, tenants get kicked out, move in with the rellies and the place goes on the market
"University of Otago public health professor Philippa Howden-Chapman said overcrowding was the single biggest housing-related cause of poor mental and physical health."
https://www.stuff.co.nz/life-style/h...ing--economist