Never enter your password into a website that doesn't use https.
To fair though, there are very few situations where the network is completely trustworthy, like your home network with no one else on it or a VPN direct to an HTTP server.
A really really untrustworthy network could MITM your SSL connections and impose itself in front of all of them (Cisco IronPort?) but I think even then your browser will complain unless you've installed a proxy that allows it or a custom root certificate.
It’s not enough for the network to be untrustworthy for MITM attacks, they have to use a certificate signed a by root certificate that your computer already trusts.
Organizations with those IronPort gateways use device management and Active Directory policies to pre-install a root certificate into your OS. The IronPort decrypts the original server then re-encrypts it with its own certificate to your computer.
If you used a non-organization managed device on those networks, it would show big scary warnings before letting you visit any HTTPS site that the certificate issuer is not trusted by your computer.