But to attack your admittedly cherry picked example, I guarantee that the US government wouldn't fault Bill Gates, they would help him out and track the money that he transferred and turn it against the terrorists.
By the way, another other dark side of making paying ransoms legal is that transferring money to a terrorist group (just because they support it) now has a plausible deniability: "Don't blame me! It was just a ransom!"
Most these "what ifs" get close to solutions in search of problems. Instead of ensnaring innocent people in the hopes of catching people who intentionally commit fraud and fund terrorism, let's use the laws we already have on the books to do so.
Edit to address the bitcoin issue: While a bitcoin transaction is hard to reverse, knowing the wallet addresses of terrorists and being able to track their bitcoin transactions would be a huge win for the good guys. And when that bitcoin inevitably gets turned into useful currency it will be another opportunity to track them. I don't think ISIS would move a billion dollars through bitcoin anyway, they'd probably pick a different method. That kind of transaction would be super hard to deal with and the network would get stressed to the point that trying to sell a billion dollars worth of bitcoin would ensure that it would be worth a lot less than a billion dollars.
Only if you assume that federal law enforcement agencies are a bunch of rule-following robots incapable of rational deduction.
It seems weird to talk about ‘making ransoms legal’ or ‘allowing ransoms to be legal by default’, as if someone has decided it. That’s not how laws work, at least in the US & EU. Laws can only limit rights, there aren’t any default restrictions.
Italy tried to make kidnap ransoms illegal, and it’s controversial, but there have been some high-profile cases of it backfiring. https://www.independent.co.uk/news/kidnap-makes-an-ass-of-it...