Well, there are pros and cons but one of the issues I see, living somewhere that has dirt cheap council homes for some poor people, is it breeds huge resentment against low income earners and causes people to focus on "this development needs to be X% affordable" and totally ignore the question of "why are we not making the average home affordable instead of focusing on some lottery for the poor?"

But, of course, the political incentives are aligned to encourage homes becoming ever more expensive at the behest of homeowners.