Plus since time immemorial the first few years of a house purchase you are in negative equity territory anyway. Quite a normal thing with all investments anyway. How on earth can you take a short term view with possibly one of the most long term investments and discard the idea that this does not happen with shares.Such a ridiculous argument.
Where the problem comes in is when the negative equity is big enough to mean you owe more on the mortgage than the house is worth and you need to sell. Most who buy their first home usually live in it for many years and usually is not an issue.
