Pamella - you are also misunderstanding the RTB discount system, and Tim is misrepresenting it.
RTB does not result in social homes being sold off for "massive discounts" in the vast majority of cases. The average discounts offered are modest by comparison with the total amount that the tenant pays for the property - enough to make the purchase feasible for an ex-social tenant who otherwise would be unable to afford to buy a property in the open market.
The value of the property "on the books" is always significantly less than the property valuation for RTB sales purposes, which is based on the market value of the property. The discount received is proportional to the total duration of social tenancy the tenant has been in, i.e. proportional to the rent the tenant has paid into the social housing system.
So, in selling off an older social home which has probably already virtually been paid for through the rent received from it over many years of social occupancy by the tenant to whom it is being sold, the provider receives a significant chunk of extra capital to put towards the construction of a new property - that is capital that the provider would otherwise not have.
The no-RTB option would have existing tenants remaining locked into their social homes and refusing to budge because to do so would lose them their established home and all the benefits that living in it brings to them, plus no new capital injection to help build extra homes.
All in all, the RTB route is better for promoting new housing availability than not selling the homes and having them blocked for decades with sitting tenants.