How public should a public key be allowed to become?

ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAtKYac1ZiC43jF6BdclPok0Yv2g4YecBVJ6a7qggOSGjRAxh2cckwCBUR6VoVc2vmt9tcHCLWuVVpKUTUynbMdWq8wOdbK7Ud7n63cpg1PL44Hg9Wn2kT/aJdMMABSE5wSNsffxslcoUhF4h0mHaf+X6E5IKVhhHsy2g1yeoc2//0Q5YPt5Kj72VY1j3aeZ8a/tqSHu5rZpFYDddnv0ARWIgSvh7jUudKT9phLUiryX9TCyGVKFCrvVKwexjAmOz63pvWtX0TJughWskvDP1ZREkhjkxtCxofwn0NG1QSbbEgGYBLf3T1Pgfkhx83Uce01Aw1hBqdl228NRg0cv0KaQ==

There is a reason it is called a "Public Key" It is ment to be let out into the wild. the worst that could happen is that someone could encrypt files in such a way only your private key could decrypt it.

Now if you lose you private key ... that is a whole 'nother can o worms.

For PGP, whose encryption is fundamentally similar to what SSH does with public keys, public key servers are offered. Through them, the goal is to propagate public keys as widely as possible.

It's infeasible to reverse-engineer a private key from a public key. In fact, that's the whole point of public-key cryptography: given appropriate key lengths, it just can't be done, and the data will be secure no matter how widely the public key is shared.

(Note that "it just can't be done" is dependent upon certainly widely-held assumptions about higher mathematics not being proven false. But if that happens, you'll have bigger things to worry about...)