The problem is not their personal fortune. Nobody has a problem about taxing their bank account. The problem here is that they're taxed as if the value of their company is a personal fortune. Thus, money that actually exist in the company will have to be extracted in order to pay a personal fortune tax. You can't actually start to sell off doors and windows to pay taxes. But that's what sometimes happens - otherwise there's no money. And where there's money, there's less money for research and investments etc.
Most (but OK, not all) ultra-rich people will be diversified and hold some of their wealth in securities, real estate and other assets. They'll have family offices and expected rates of return, they can arrange for enough of their wealth to be liquid to pay the taxes... they just don't want to.
Given that wealth tends to appreciate around 4-5% (ok that's Piketty - but pick your favourite number) a 1% wealth tax is a "moderate headwind" on wealth growth for the very rich.
On the other hand, I agree the founder on 1st company with most of their wealth tied up in it is in the worst position, and also that the threshold in Norway seems very low (170k USD) and would hit many small business owners - who also will find it much more difficult to change their tax residency than the truly wealthy :/
Selling off securities, real estate and other assets is extracting wealth from companies.
One reason the general ROI of generalized wealth is higher than 1% is because the sort of people who accumulate it are allowed to do so without it all being taken away in taxes, so they're incentivized to grow their investments. The assumption that average ROI remains constant even after changes to the tax system is the sort of bad economic modelling that the article criticizes, and apparently someone won a "Nobel prize" for (economics isn't AIUI a real Nobel prize) just for pointing that out. A lot of rich people are rich on the back of investments, so clearly if they leave there are fewer people around creating that 4-5% to begin with.
You're right that wealth taxes interact very badly with startups. In fact in Zürich, Switzerland they had to adjust the wealth tax rules because it was basically killing any chance of a US-style startup scene. The moment you raised money from investors you would be considered really rich, not just paper rich, thus forcing the company to give huge payments to the founders so they could settle the wealth tax, and those payments would themselves be considered income immediately pushing the founders into the highest possible tax bracket, etc. Even if they're actually living on ramen! Unfortunately the fix for this took the form of the government granting special privileges to companies classed as "startups", which leads to a strange bureaucratic process in which the taxmen try to decide if your business model is "innovative" or not, using some internal definition, because "startups" are defined to have "innovative" business models. This is well beyond the scope of what a tax official should be deciding IMO, but it's the kind of thing that seems inherent to trying to implement a wealth tax.
