How secure is calling bitcoind JSON-RPC from same computer? I am wondering if calling JSON-RPC from the computer it is running on is secure. I read How secure is calling bitcoind JSON-RPC? and understand why it is insecure to do so from a different computer.

Is there a secure way to call it from the same computer without using SSL?
Yes. By default, Bitcoin will only listen for RPC connections on local loopback. Local loopback cannot be accessed or spied upon by another computer.