Sign arbitrary data with your SSH keys

I get that they're "public" keys, but I was surprised to learn (and from somebody other than github themselves) that ssh public keys are just available at that github.com/username.keys URL (without there being an option to disable it, it seems?). Did most people already know that? Probably fine but just surprised. Just tried searching their authentication docs [0] and I don't get any results for "public key url" either

https://docs.github.com/en/authentication?query=public+key+u...

Why would you want to disable it? They're not 'scare-quote' public, they're just public - analogous (kind of craply but workably) to 'distributing' your face, but not your passport/driving licence/etc.

The private key part is secret of course, never shared (that's where the analogy above breaks) but the public part is fine and desirable for everyone to have access to - that's how they verify that you signed something with your private key, how they encrypt a secret message to you.

Because they may be used to learn the identity of an otherwise pseudoanonymous github account if one uses the same keys with another account that is tied to his real identity.