As someone who's done the round trip on the residential mortgage - aggressively paying it off fully then taking on a new one - from my point of view these days I'm pretty firmly in the camp that most people who can safely do so should hold some mortgage debt, provided they have all the other aspects of their financial life already lined up and ticking along nicely.
How much this is of course highly variable from one person to the next and depends on the usual factors - your income/saving rate, your existing asset base, your current amount of equity, and of course your risk appetite. Nonetheless it is amusing and even baffling to me that some people will be happy to hold a lifetime's worth of investments in a 100% equity portfolio in an expensive market while insist on zero housing debt. Personally I would rather hold a less volatile portfolio with some modest financial gearing while being able to sustain a high saving rate from our incomes. That, to me, is the sweet spot.