There are several things I have learned independent of DR or anyone else that has a published opinion. One thing is there is no such thing as good debt and bad debt, rather what we have is degrees of bad. Another, even DR will allow a home mortgage as long as you put 20% down of a 15 year fixed, the cost is no more than 25% of household income and you strive to pay it off as quickly as possible. This is an important part of living below not above our means.
I have spent much of my adult life thinking that being debt free was impossible, but it is possible because I’m debt free. Like you I don’t care what anyone else does with their money, their mistakes are not my worry. Having said that I personally think it is a huge mistake to retire with any debt, mortgage, HELOC because things can go sideways on a moment’s notice and without advance warning. Secured debt means you co-own your stuff with a bank and that bank can take possession of your stuff if you are $1 in default. That $1 gives the bank controlling interest.
Respectfully, would you say that even with my statement: "So if anyone is going to be like me instead of you and have a mortgage debt, that's fine, they just can't count themselves as wealthy enough to retire unless the investment balance is also enough to pay off the mortgage at any point they have the need to be debt free (i.e. if I one day get tired of the bank's rules of my house and want to separate myself from the bank by paying off the mortgage that day)." ? Basically, I'm with you on the need to be debt free (at least at a moment's notice if the need arises), but I'm not ready to be all in on the debt-free-is-the-only-wise-way-to-retire mantra.
Likewise, what about inflation? Isn't it wise to keep a healthy portion of your net worth invested so that it gains enough to offset inflation? Of course, real estate usually gains, so there's that. But that real estate wealth you live in can't be utilized to help pay for food and such (fight inflation) unless the real estate is sold (or mortgaged). One of the real problems that "goes south" is the cost of living (inflation) going sky high. That's not a hypothetical or an every now and then problem (like a market downturn). That's an every year reality. I see that with my 82-year-old mother who's been retired for 20 years with little increase in her SS check and state pension, but much increase in her cost of living (groceries, home energy costs, gas for her car, even "cheap" entertainment, and of course medical costs). Plus, even if real estate is used to help fight inflation (i.e. sell your home as part of down-sizing anyway frees up some money from your home wealth), I'm uncomfortable with too much of my wealth being in one bucket (real estate). I'm not dissing real estate, I'm just saying don't be too dependent on it (expecting mainly asset increase in home value being how you fight inflation in later years when you downsize and sell your home).
By not using one's wealth to pay down the mortgage (particularly if we're talking about people with 3% fixed interest rate mortgages before the recent rate hikes) and instead using that wealth to build a diversified investment portfolio, your portfolio can be something you withdraw from annually for cost of living. But it grows most years (thus your withdrawals grow). And by being heavily diversified it can handle market downturns (as you put it "head south") while giving you a steady income stream (even with housing prices dropped bigly from Oct 2007 to Mar 2009) two favorite asset classes of mine (long-term US treasury funds and mid-term treasury funds) were up 14% each (if I had been retired I could have done my annual withdrawals from them). Likewise I could have pulled form the two money market funds. By the end of 2009, even a couple of equity funds I like were up (a global real estate fund and a large-cap core fund I like) were up 20% from Oct 2007 (having more than recovered their 2008 losses). So those funds can be where you did your 4% annual withdrawal from even though much of the rest of the portfolio was still "south". So this is an example of how even when things head south, they don't all head south at the same time if the portfolio is diversified enough.
Thus IMHO, a diversified portfolio reduces the fear of going into retirement with a mortgage, but frees me to have more of my wealth invested (vs paying off the mortgage) so that my investment gains in the good years can try to outpace inflation. That keeps me from being like my mother, who is debt free, but has to live on a tighter budget than she'd like because inflation is eating up her income.
Please don't take this as a diatribe against those who insist on being debt free going into retirement. I get that, and I think that the people who do that are better off than most people. I just typed up this explanation of fearing inflation more than debt since you used the phrase "huge mistake to retire with any debt". Well, maybe if the debt was to fund a lavish lifestyle. But not IMHO if the debt was used to fight the very real problem of inflation.