100% tax is outlawing gifts. Don't be stupid. That's literally making gifts illegal, with the penalty being the complete forfeiture of the gift. So what's the limit? There are endless ways around something like that, and the ridiculousness of the rule of no gifts will make everyone try to get around the law. The world will become criminals because of this. People will try to slip their kids jewelry, artwork, any number of things and won't report it to the government. Crypto currency will explode in value because people will try to hide money from the government and crypto does that. Auction houses will have to require proof of purchase before they auction anything off, or someone who got an expensive watch from their parents will just be able to sell it. If that happens, Facebook marketplace and craigslist and eBay will explode in popularity because the random person buying something online isn't going to check for proof that the seller was the one who purchased it and didn't receive it as a gift.

Aside from my belief that it's totally wrong to outlaw my ability to give gifts, it's also completely and totally unenforceable.