I think the rationale is that if you have unrealized gains, there is a high likelihood that you are well off, and can therefore be pressured into reifying your economic potential into a resource that the government can appropriate (ie money)

It’s not a straightforward tax like income tax, it’s more of a class based tax that has some aspects in common with income / CG taxes.

It makes sense when you consider that the capital owning class is and was always the most well off, even more so than aristocrats, since the Industrial Revolution anyway.

I think the issue that these laws are trying to solve (and perhaps not with sufficient nuance) is that the ultra-rich get paid in stock or options, which then go up in value. Those "unrealized gains" aren't taxable (because they're only theoretical at this point), but they're still able to go to the banks and borrow against those gains anyway to fund their lifestyle tax-free.

Obviously you need to be a bit sane about it; I have "unrealized gains" by virtue of having stock options in a company, but while I'm paid well I'm definitely not rich by any stretch. I'm just some dude with stock.