The way the law works is often by banning based on intent and meaning and content. Exchanging information is too general: the law looks at what information, by whom, for what purpose.

Nearly every white collar crime fundamentally involves some sort of unauthorized communication. (Insider trading, for example, involves receiving information by virtue of a trusted position and then communication information to a broker which causes them to execute trades on your behalf). We can even get beyond white collar: hiring a hitman is obviously illegal even if it involves. communication.

I'm not saying (in this comment) crypto is necessarily bad. I am saying you need to defend it on the merits; it's just info so it's ok isn't how anything in society works.

By that logic, most financial crimes are just people signing and exchanging pieces of paper.

They're not just exchanging information they're exchanging something that, by their very own account, has financial value. We as society figured out long ago through hard real life lessons that there must be sophisticated rules and regulations around financial transactions or else enormous negative consequences and human suffering follow.

Crypto is the same as introducing your own currency and printing your own notes. "But it's on the computer" doesn't change the nature of it.

It depends on the specifics.

For example, suppose a drug cartel invents a new formula. The DEA gets to ban it under existing law.

I'm not saying that's analogous. I'm merely providing a counterexample for your idea that the government always has to create custom laws whenever something new happens.

Crypto itself isn't illegal but why is it different? A real bank needs banking license and regulation and yet an "exchange" doesn't.

Unregistered securities are illegal.