Should unrealized capital gains be taxed?

My parents own a small apartment building, and I have watched them argue with the county every year about what it is worth, because appraisals are opinions with letterhead. Now imagine the IRS doing that annually for every private business, art collection, and family farm in the country, with penalties if their opinion differs from yours. France tried a wealth tax and repealed it in 2018 after economists tied it to capital flight, and several other European countries walked away from similar experiments for the same reason. Valuation disputes would flood the courts, compliance costs would crush exactly the mid-sized businesses the threshold supposedly spares, and the revenue projections would melt on contact with reality. A tax the government cannot measure fairly is a tax it cannot levy fairly.