The argument being made originally was that asset price inflation in the housing market was a bad thing.
However, house mortgage rates are lower than marine and car finance rates for example, primarily because boats go down in value. Therefore the loan is riskier as the lender's potential loss due to default risk increases over time on a boat/car and reduces over time on a house. Next we have the building industry, which we can see depends on the investment increasing in value to justify the investment.
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So we need the value of houses to go up, in order to create the economic environment for house builders to build and home owners to invest.