You likely mean .ssh/id_rsa (or perhaps .ssh/id_ed25519). The .pub variants are safe to share.
Of course I updated my OP.
reminder to use a passcode on your private key with ssh-agent.
what's wrong with RSA?
The original poster refers to sending your SSH private key, not RSA. Your SSH private key can be used for very malicious purposes. For example, if you use Git over SSH to upload code to your remote Git repositories, someone malicious can take your SSH private key, and hijack your Git repositories.
Oh I got it, the nasty part is nabbing the SSH private key, not the fact that it's RSA... duh :)