So what we can have in the free market, when interest and risk is zero, is the cost of administration, payable by you.
The negative rate that ECB is talking about, is the bank's deposits in the central bank, and that is not the free market, because the ECB by regulation decides what the banks have to deposit... at least to some degree.
No read the article again. He cites some cases of corporate bonds a negative interest rate
Searching for reasons, I found rules and regulations. In my opinion, this is non-free-ness. He also pointed to bonds as safe, and that can mean two things: Safety againts default, and safety against theft. Safety against default: nothing is more safe then the actual money in your mattress. Safety against theft is the money management aspect, discussed above. So it still holds that negative interest rate, when you remove the money management aspect, is impossible in the free market.
In a non-free non-market, anything is of course possible, it can not even be discussed sensibly how it works economically.
So, example from the text, If some pension fund is coerced into owning a commercial bond with a negative interest rate, how is that not robbery?