Modern medicine can also be like blackmail. Nobody has to actually threaten you, but nature will kill you unless you pay whatever the price of treatment. That's why we need competition, and why pharma companies like monopolies.
https://en.m.wikipedia.org/wiki/Pharmaceutical_Benefits_Sche...
The blackmail version is actually "Refuse, and we'll produce a generic version locally and perhaps even export it to any country that wants it."
Note that a mixed economy (combined public/private funding, like the french and australian systems) are probably for the most part the most economically efficient. A big problem in australia is over-provision of services, especially ending up getting more pathology tests than strictly necessary.
So in this threads context, "hey I found a vulnerability in your infrastructure, you could pay me for it" does not actually constitute blackmail unless they actually follow it with "I'm selling to the highest bidder which may not be you".
This makes the company with said vulnerability pay the true price for it - may be even just purchase it on the black market and outbid the "bad guys". Or pay someone to fix it asap before it's sold.