If a "google.com" request is MITM'd because it's not encrypted, then the MITM can do all sorts of extra damage, using that as a platform, to sites like "mail.go

If a "google.com" request is MITM'd because it's not encrypted, then the MITM can do all sorts of extra damage, using that as a platform, to sites like "mail.google.com" Hence when google.com is forced over SSL when you're logged in, but not forced over SSL otherwise.