The Ontario government changed rent controls with the aim of protecting existing tenants. But the policy change allows landlords to raise rents for new tenants. The unintended consequence provides landlords with incentives to try and get existing tenants to move. This may lead to reduced maintenance, ignoring tenant rights, and other actions designed to harass existing tenants.
The other key argument is that as long a condo construction is more profitable than building apartment buildings, even if rent controls were eliminated, there is no indication that developers would build more apartment buildings. The author suggests that the only large increases in the supply of rental housing have come from government subsidies for building. Other policy options are loosening restrictive zoning laws to increase profitability, and housing vouchers for the poor (to eliminate another unintended consequence of rent controls in benefitting higher income families who could afford higher rents).