... you expose your private keys to your Bitcoin wallet the same way that you enter a pass phrase to login to your IOTA account.
No, you don't. At no time do you expose your private key. You enter a password, so your wallet is password protected (which IOTA cannot do). And that's it. The private key stays private.
so myetherwallet is not safe because u can login with just some random characters and u can't protect it with password