My point was that removing rent control did not stimulate the development of new rental units, affordable or otherwise. This was something suggested by many people who argued for removing rent controls.
Market rules would suggest that as availability becomes scarce, the prices will go up. As you have pointed out, rental housing is a business; a business which could effectively squeeze the lowest income earners out of their apartments as scarcity increases and prices rise. Many low income earners typically don't own cars and can't afford to move far outside the city to seek less expensive housing. They get cornered between incomes that don't keep pace with the cost of housing, and a limited selection of alternatives. Moving becomes difficult, if not impossible for some, as the price of a new unit could rise considerably when compared to the constant annual hikes in rent in their existing unit.
Rental building owners and managers view forms of housing geared to low income earners as an attack on what they perceive to be their rightful business, so I am not surprised when building owners are opposed to rent controls of some sort, or to other low cost housing options.
Rental buildings owners can write off losses, and can certainly write off the cost of improvements to their units. They can also pass the costs on to renters. They can pass on increases in the cost of heating, and need not adjust the increase once it is in place. This is exactly what happened when gas prices spiked a few years back, then dropped. There was no rent increase reduction when heating costs fell. Is the system totally fair to a building owner? No. Is the escalating price of housing fair to low income earners? Not by any stretch.
The issue of housing is crucial in society. Its impact extends far beyond the right of a building owner to extract a profit from a renter. We don't have a particularly strong policy concerning guaranteed low income housing, and there has been little effort in pursuing unique or inventive forms of housing to deal with the needs of low income earners as a group. Some fear the creation of ghettos through the pursuit of co-ops or other housing that addresses the needs of low income earners, but this is a straw-man argument. Low income earners are already "ghettoized" by their small incomes. Either we should seek out housing alternatives or maybe start defending large increases in income.