How is someone getting hold of my secret key dangerous? If my password is strong enough they still won't be able to decrypt anything because they won't know the password. If it's like, 30 characters long and a random string of upper and lower case, numbers, and special characters then they won't be able to crack it. I realize it's better to keep it out of anyone's hands though, just curious as to what someone could do with it if they have it though.
BTC. If I have you private key I can regenerate your wallet, recreate a password and move your BTC. Doesn't matter how long your password is, because I will recreate the password to 123456 so I can remember.
PGP. Your password could be "password" and everyone could know, but without access to the private key, they couldn't begin to crack it.
If someone gets a hold of your BTC private keys it will be a bad day for you. You will be fine losing you pgp keys unless they know your password, or they can crack passwords. There is no reason you should give either to anyone and for any reason.