For Ethereum to become a real financial tool, that you could use in place of credit cards and cash, it needs privacy.

Like the title says, for Ethereum to become a broadly useful financial platform that can be used in a significant fraction of financial interactions, it absolutely needs privacy. Tragically, the US DoJ has decided to prosecute developers who provide general purpose privacy tools on account of the fact that criminals will use such tools as well: that's the primary rationale provided by the DoJ for indicting Tornado Cash's open source developers.

And the plausibility of their arguments about Ethereum based smart contracts being within their purview to prohibit comes down to something as banal as aesthetics. ZCash's zk-proof logic and Monero's bulletproof logic are both off-chain, so regulators and prosecutors don't misconceive it—or can't misconstrue it—as an address that holds funds, the way they do with the smart contract addresses that hold the Tornado Cash logic that users call to encrypt their transactions.