I don't think the analogies to encryption are fair because a Tor exit node is far more active in shielding criminals than the inventor of a new cryptography scheme is. The inventor merely puts out an idea that can be used for good or bad. The exit node operator is actively paying on an ongoing basis to shuttle CSAM and bomb threats.
The exit node operator is also shuttling other content, so it's not wholly evil and on the balance someone might decide it's still worth it, but it's still a much less obvious ethical call than simply designing a piece of tech.
Someone has to pay for distribution, maintenance, and integrations of the encryption on an ongoing basis. If it was legal to write encryption but illegal to distribute it, what would be the difference from a ban? Both tor and cryptography require an ongoing effort to provide their service.
I see a pretty strong difference between hosting the latest build of gpg and actually running a server that moves the bytes that cause the harm. You may not, but I do.
The exit node operator is also shuttling other content, so it's not wholly evil and on the balance someone might decide it's still worth it, but it's still a much less obvious ethical call than simply designing a piece of tech.