Hmmm, LA Aussie it is an interesting one. But to be retired and living off my investments I believe in paying down debts to a suitable level that income exceeds debt. without that there's no retirement. And non deductible debt is usually linked to $0 income because you live in the house. Hence I don't believe in non-deductible debt.
I am all for tax deductible debt though and I believe in using debt as a tool to make suitable returns.
One thing I have learnt about myself more recently is I can't just buy places and sit and wait for capital growth etc. I always have to be renovating, subdividing, developing etc because that's what I find to be enjoyable and fulfilling. And doing that usually requires me to carry decent debt - just that it's all deductible.