If someone just wants to create something they like, and then own what they created, a big corp or rich jerk could easily bankrupt them through the tax/force them to sell it off.
Some things don't need to exist in the context of a market and markets are often less efficient than folks seem to assume.
If you own 80% of something worth $1B - you have $800M. If you can't sell $2M at your preferred price to pay your taxes, then it's not worth $1B, and you wouldn't have to pay that much tax anyway.
But the whole point is that you don't _want_ to sell it. And it's entirely possible to own something that is work more than 20x (given a 5% tax rate) than you currently have in accessible cash.
For example, assume you write a story and MegaCorp decides they want to make a movie of it. Right now, they need to pay you to license it. With the Harberger tax scheme, they can force you to sell it to them; because you don't currently have the money to pay taxes on what it's worth to them.
1. Private — untaxed, lasts for 14 years (or until the death of the last author), goes into Public Domain. No need for registration; and,
2. Public — any work (before it's expired) an be transferred to a Public work. At that point some sort of Harberger tax scheme would kick in.
Obviously, picking a number like "14" distorts the market — works that take off after 14 years are going to be undervalued, which sucks. OTOH, the point of copyright is that the opposite distortion — free-for-all — is considered bad.