Extra emphasis on “of reasonable value”, because you seem to need a little assistance with your reading comprehension since you’ve ignored it literally every single time I’ve said it,

Because the entire housing market is unreasonable in almost every city in the Western world. It's not just a few outliers here and there that can be compared to some average. The average itself is completely out of whack. We can't just rein in the crazy part of the market; the whole market is crazy. Either we pick a semi-arbitrary value and tax above that (your plan) or we introduce a graduated, progressive tax on all homes (my plan). Introducing exemptions and especially benefit cliffs has historically always had crazy unforeseen negative consequences. A tax on all homes will by itself automatically bring the market closer to equilibrium.

The average home price in San Jose, CA is $1.4 million. That is crazytown. We can't look at that as a benchmark to try and bring prices in line with.

Moreover, I would argue that anyone who owns a home at all is already of enough means that they don't need tax breaks. Proportional to your equity obviously, someone who just closed on a house shouldn't be slapped with a tax bill based on the whole value of that house. But we have a 0% income tax rate on the lowest incomes because that income is essential to living. Home ownership is not essential. Having shelter is essential, which is why I support taxpayer funded grants to homeless people etc, but home ownership is not and should not be a fundamental right. If you can afford to buy a house, you can afford to pay taxes.

I might see your point if Social Security payouts were substantially increased, but they aren’t, and you aren’t proposing that we change that, either.

Housing policy is already a big enough conversation. Incidentally, I actually support universal basic income, which you could look at as substantially higher social security payments.

But relevant to this conversation, social security in its current form is not a pension. If all you're living on is social security, you probably can't afford to retire. If you're physically unable to work, then that's disability. If you don't have enough money saved up to pay for the life you want, but happen to be age 65, you're not retired. You have to keep working.

I haven’t mentioned Prop 13 once

Mathematically, it's close enough to what you're advocating for: a tax carve-out for homeowners, incidentally with the same tear-jerking "old people forced out of their homes by evil taxes" argument. It has the same supply-demand effects as well.

So, to summarize:

I'm ignoring your "reasonable price" point because it's either arbitrary or unworkable
I'm ignoring social security because it's not a retirement plan
I'm equating you with prop 13 because the socioeconomic effects are essentially the same

Instead I'm addressing the core of your point, which is that homeowners should not pay taxes on their home (within reason, mansions etc excluded). To which I say, "yes they should, all of em". Again, if you have enough money to buy a house, you have enough money to pay taxes. If your house increases in value such that you can't afford the taxes anymore, fucking congratulations, you just made a bunch of money. Now you get to experience the pain of renters being priced out of their own neighborhoods, but also with a small golden parachute to take with you. And it makes things less bad in general for everyone by helping to bring housing costs down across the board.

Also, just to keep this conversation in perspective, I don't think this is the MAIN reason why housing is crazy in places that have similar tax carve-outs for homeowners. I actually think that's zoning and local NIMBYism. But this definitely contributes a fair amount.