In the first place, it advantages folk who are paying far less rent than those who have to rent in the private sector. They should not then be able to buy the houses at a cut price, while reducing the stock of affordable housing. It isn't as if we have an oversupply of such housing and it really isn't fair!
People in affordable housing should use their advantage to save a deposit and buy on the open market, like everyone else has to do which would free up their housing association house for those who need it.
We need more affordable housing not less. We have families in bed and breakfasts.