I’ve recently begun categorizing our principal payments as savings instead of spending. A house is stable-ish asset and the result of a principal payment is a transfer of assets from cash to equity. Plus I categorize extra payments as savings, I’d have a hard time considering it otherwise, so why not the entire principal payment? Also I expect to have the house paid off by the time I would consider myself financially independent, so the expense is not a good baseline for future spending. I guess by that logic neither is the interest, but interest is more clearly a lost expense once I pay it.
A house is not edible, as some would say, but it does provide half of the food/shelter necessities in life, so all savings into the house are saving toward ridding future obligations related to your shelter expenses. This debate is unlikely to be settled any time soon, I only wanted to announce the side of the fence I fall on… for now.