This is actually an incredibly false point. The royal family (if treated like anonymous land-owners) would cause a sudden and drastic drop in fundraising within the UK. Assuming their property wasn't seized having them retain their current station is actually a net positive to the British tax-payers - they lose far more potential income each year in free land leases and charitable donations (known collectively as the Crown Estate) to the state then they receive in benefits (known as the Sovereign Grant). This arrangement is financially detrimental to the royal family in terms of absolute value.
You are completely wrong on the basic facts of this. The Crown Estate belongs to the state, not the royal family. The Sovereign Grant is an arrangement to pay the monarch is paid 25% of the revenue, which would otherwise flow to government coffers like the rest of the revenue. Were the UK to become a republic, the state would simply stop paying this to the monarch, and thus gain revenue.
I mean… why would the royal family be allowed to “keep” anything in an abolished monarchy? Obviously you should just seize roughly all the property. It’s a product of the State, not the royal family working hard
Maybe? That's a really complicated question honestly - how much of their personal property actually is hereditary wealth and how much is a benefit of their station. I can tell you the answer is neither 0% nor 100% - the royal family (if dethroned) shouldn't be thrown out as paupers and it shouldn't be granted personal control of spaces that enjoy public use. Where precisely that line should be drawn is complicated but if that line leaves them with any significant portion of their current titular wealth the UK will end up losing money. The Crown Estate might be worth around 15.6 Billion, so a few hundred million every year is far less then the family would receive if they liquidated the lands at value and just invested it into an index fund. The actual income of the estate is significantly higher - with a lot of those assets under reporting their actual yield in terms of tourism and public benefits.
I think it's a really complicated question.
Lastly, while we're on this topic - why hasn't the US seized the wealth of the 100 most wealthy individuals unilaterally - that money would be of immense amount of benefit to the country so why do we let wealth accrue?
It's a complicated question with regards to some of their property. It's not at all complicated with the Crown Estates. That is clearly public property. Otherwise Edward VIII would have kept it when he abdicated.