Hold the phone. Public WiFi is where you want your connection to be encrypted at all times. A WiFi login page should be encrypted without scaring the user just because its certificate is self-signed. Beyond that, any connection that is encrypted on public WiFi is better than one with no encryption. I don't care if I'm looking at pictures of dogs and cats; it's not the business of other people on my network to sniff my activity and see exactly what I'm reading, even if they can see my DNS activity. Users aren't in control of whether a site supports HTTPS, thus it's a courtesy, given the ease it takes in implementing HTTPS, that even "innocent" web services do so.