The counterpoint is that the valuation seems to be a fiction when it could represent a liability, and a real thing when they want to, say, take out a loan against it. It's awfully convenient that it is selectively fictional.
It's not, it is inherently fictional to all. When you want a loan you will have to put up significantly more than the loan amount as collateral.
Note that for more humble "wealth", folks are taxed. If you own the house you live in, even if you are not using it as a financial instrument but just a place to live, you get taxed on the unrealized "value" of the house. I don't get to say the market value of my house is a fiction since I'm not selling it.
(1) That tax appraisal value is often significantly less than the retail appraisal, and tax appraisal often stand for many years without adjustment. However if retail value decreases a homeowners can generally request a reappraisal.
(2) Both the more modest and the wealthy are subject to this.
if you live in your house, your property tax is subject to the standard deduction, which means folks generally don't get a deduction for it.
"Don't take" not "don't get", the homeowner gets to choose to use the standard or the itemized, whichever is the larger deduction.
If you own a house that you rent out to someone else, the property tax you pay is not subject to the deductible, and you can deduct it.
No, it is a business expense that gets deducted from business income. Renting is a business activity.
The tax system rewards landlords more than homeowners.
The preceding calls into question the logic of your determination.
It seems that either you assess a property tax on net worth analogous to what is imposed on common folk
We do. Homes are taxed. Stock valuations are not. Wealthy or common.
or at *least* tax loans against such assets that have nothing to do with paying for that asset.
The interest on those loads is taxed. The spending of the loan amout is taxed via sales tax.