It doesn't.

> How does being required to track data about taxation challenge the existence of the builders you mention?

Suppose US law says that it is illegal to "mine" a block of bitcoin unless you keep records of the true name, address, and social security number of every person whose transaction occurs within that block and provide that information to US banking regulators on demand.

Since the information available to miners does not include true name, address, and social security number, the only way to comply with such a requirement would be to not mine blocks for bitcoin.

(There's another option -- go ahead and violate this law. If the US government doesn't have a beef with you then they'll just choose not to prosecute you. If they DO have a beef with you then you can try arguing in court that the law is unconstitutional. This will take years and extremely large legal fees and it might or might not be successful.)

I don't have a problem with requiring Coinbase or Biance to maintain records of information available to them. I DO have some concerns with mandating that no transactions may be done anonymously except those done in cash -- although I understand that some may disagree on this. But I strongly oppose imposing impossible-to-meet requirements on those who write code for cryptocurrencies, perform "mining" of cryptocurrencies, or who hold and/or spend cryptocurrencies themselves.

I guess I was too elliptical, because I mostly already understood what you've explained here - I thought the OP was making way too strong a claim.

Instead of just saying that, I asked why he thought the builders in question had their existence threatened.

The builders in question may not be able to legally build the systems they want to in the US, but that's really not threatening their existence.