Mortgage is leverage (debt) and that can be bad. When you buy a house you speculate, to some degree, on the price of the house. I am sure a no-arbitrage condition exists in the housing market so your guess regarding housing prices in 10y is as good as anyone's.
Also, the point about diversification is a valid concern. Would you put (50% of your net worth + loaned money) into only FB/AMZN/XYZ stocks, today (tomorrow)? Probably not.
Also, the point about diversification is a valid concern. Would you put (50% of your net worth + loaned money) into only FB/AMZN/XYZ stocks, today (tomorrow)? Probably not.