How do you propose to deal with the complete economic meltdown that would occur, when people with mortgages end up with massive negative equity and can't sell their homes? Then lets look at the loss of income from the state due to inheritance tax and lastly the extra burden on public services as people are no longer able to use the proceeds from the sale of their home to pay for their care.
Its fine to want to slow the growth in house prices, but to have a policy that reduces them by 50% is beyond daft.