[marc3842h]

I do agree that encryption is especially required on public WiFi networks. But WiFi login pages error because they mitm your current, encrypted connection. Your proposal would additionally add an error in a case where the user especially chose a http site to not receive a error because they're getting mitm-led. I never had any wifi login page that used a self signed certificate.

[RandomInteger4]

Then providers of public wifi need to stop using a MITM to provide wifi access. This is an opportunity for better technology to be developed or implemented or made easier to implement or whatever.