> But let's not pretend that there's no precedent for taxing unrealized capital gains.

Are you mistaking property taxes for something else ? Property taxes are imposed on property value and have nothing to do with the gain or loss in the value of the property.

But if you want to apply the same parallel to stocks then I think we should call it 'wealth tax' rather than anything to do with income and do not tax the gains (realized or otherwise) but the total value. So if you buy a stock worth $100 and it is $50 next day you still pay $0.5 as taxes even though you might have lost money. I do not think that is a good idea but that would be somewhat consistent with property taxes.