You slow down and introduce uncertainty at the very point (the start of a pandemic) when you least want to do so.
If my becoming a hunter gatherer would single-handedly eliminate 50% of global emissions or something, I would do it in a heartbeat.
Moderna is a public company. It will cost them, at current time, $134 billion.
You're picking on one entity here and asking them to give away everything. Moderna is a company that originally intended (and is following through on) developing cancer vaccines.
If Moderna's money goes to competitors and they lose cash flow, their ambitions here become harder if not impossible.
Also ask yourself why the WHO hasn't developed a vaccine for Covid and cancer by itself. It certainly has the funding to do so.
Ask yourself why European countries aren't dishing out money to buy Moderna and open up the patents.
I don't mean to criticize you, merely to get you to think about the interlocking and competing world-scale problem gradients. Nothing is ideal. There's always a bigger picture, and you have to think pragmatically.
But also, in any discussion of "why doesn't X buy Moderna", a natural follow-up is "wait why doesn't Moderna just do this on their own if they can". Not an expert in hostile takeovers, but I'm pretty sure it would be a lot easier and more efficient for Moderna to just save the world themselves rather than wait for someone to acquire them and force them to do it.
See why that's unfair?
I'd say it's even worse given that this was their blood, sweat, and tears. An evenly applied tax would be fairer, but you're picking on the winner here and choosing for them to be dismantled. That discourages "winning". It's a very bad objective function.
The founders clearly believe they're worth more than 100B or they'd have sold out already. They have huge ambition. To cure cancers and other ailments.
It seems to me that you think the world can steer this innovation better. It's a very socialist approach. And again, I'm asking why hasn't the world solved this problem outside of capitalism? Why hasn't the WHO stepped up to the plate?
You're right that it's a socialist approach. I don't know why the WHO hasn't bought them if they can. As I've said several times, they should and I hope they do.