You would have a hard time finding anyone who uses off-the-shelf cryptography so carefully that long-term resident code on their box couldn't capture all the relevant keys. Your comment seems wishful.

People do the same segregation, between long-term non-transactional accounts and short term spending accounts, with their bank accounts. But businesses still need to keep non-connected isolated quarantined machines to access the bank.

The comment you're responding to didn't argue that wallets couldn't be encrypted. He argued that in the (not unlikely) event that a malware incident on your machine was able to compromise your wallet, you'd have no recourse. And: he's right. You wouldn't.