If you start considering active man-in-the-middle attacks, someone can modify the HTTP page that hosts the login form to, for example, also send the password so

If you start considering active man-in-the-middle attacks, someone can modify the HTTP page that hosts the login form to, for example, also send the password somewhere else. For defending against passive MITM, you're right (as far as I know) that HTTP-to-HTTPS is okay.