Kennington: I don't think 'homeowner' is a legal term - it means someone who owns their home, whether or not they have a big debt.
Negative Equity. This may or may not be a big problem. If you can afford the mortgage, paying the mortgage is likely to be about the same level as if you were paying rent. Everyone has to have somewhere to live. In the longer term the property value is likely to rise again. If the mortgage payment is unaffordable and the value is unlikely to ever rise significantly (for some reason - maybe the area took a nosedive in reputation, or the main industry providing the only employment for miles around packed up, for example) then it might be a good idea to study the 'sunk costs' fallacy and pull out before the unpaid debt gets bigger and the value sinks lower, cut your losses and run.
In the 90s when thousands were plunged into negative equity, many people rented their property out rather than sell, if they moved. The rent covered the mortgage and they paid another rental. Eventually prices rose again and they regained the valu....and in fact prices since then have been ridiculous, mostly.
The question of buying being no better than renting because 'interest is dead money'. Well yes, interest is 'dead money' - or at least needs to be calculated into the overall cost of buying, and I obviously inflates the overall paid price no end. BUT again, everyone needs somewhere to live, and if you are paying out for a mortgage you will have something to show for it. And at the same time as you are paying interest on the loan, your asset is (probably) also rising in value.
Situations where it is 'dead money':
Interest only mortgages where you have no parallel vehicle with which to pay the capital at the end of the loan. In ye olden dayes, interest on endowment policies etc was sky-high. You had enough cash at the end of the period to pay the mortgage and a chunk left over. Now such policies have rock bottom interest rates. People buy a house on interest-only, and hope that the value will rise enough so that on retirement they can sell the big house, pay off the mortgage and still have money left (lots!) to buy a smaller house. These are some of the people who will be well and truly left high and dry if there is a big price crash. They will be left owing the full mortgage, and may have none left over to buy elsewhere, and worse, may owe thousands due to negative equity. Nothing to show at the end = 'dead money'.