Earlier quoted context omitted.
The harm is that if you use the same key elsewhere, it can be linked to your github identity.
If you are needing to keep your identity hidden/ambiguous, then you need to be careful with your keys. Don't publish a public key if you don't want it to be public! These keys and the ways people often used them are very much not designed with privacy as a priority: they are explicitly for proving who you are so you can be given access to something. Key management with regard to keeping different concerns separated i…
I think it's fine as long as you _know_ github is going to make it public. The only problem is that it's not at all obvious, as can be seen in this very thread.