I don't think it's really about what end-users do with the warning, or whether they tune it out; site owners will not want a big "Not Secure" badge showing next

I don't think it's really about what end-users do with the warning, or whether they tune it out; site owners will not want a big "Not Secure" badge showing next to their page, right next to their domain / brand. This change creates a powerful incentive for sites to move over to HTTPS.