We need to protect the integrity of the information so that kit's not abused to serve malware or pages that exploit zero-day vulnerabilities to the end-user when they browse on an insecure network (which, if Snowden's publications are anything to go by, is every network).
HTTPS is not just confidentiality - security is confidentiality, integrity and availability.
HTTPS is not just confidentiality - security is confidentiality, integrity and availability.