Taxing gains on the value of anything used in a contract as collateral is a simple and useful start.

That would have wide ranging negative effects on the middle and upper middle classes (and wallstreetbets), consider HELOCs (home equity loan), ag loans using farmland as collateral, and brokerage margin loans.

I’m fine with it provided there’s some sort of minimum level of wealth required to be taxed in this manner. Taxing someone that is using a HELOC to replace their roof on the unrealized equity appreciation would be unfair, and I’m not even a homeowner.

There are better ways to attempt to tax wealth, eliminate the step-up cost basis and asset shielding in trusts and other forms of estate tax avoidance and the issue would correct itself eventually. Unfortunately, politicians in the US will not do this because they need donations from extremely wealthy people who absolutely do not want their estates taxed away. It’s also too easy to hide money in other places, there will always be nations willing to take on tax haven status to reap the benefits. I’m not sure what a practical solution is given the outsized influence of the wealthy all over the world.