I think the big point that a lot of people are raising, however, is that a "proxy which does not faithfully pass content" shouldn't be legal in the first place. Users don't want network operators to be snooping on them if they can avoid it. The fact that such behaviors are formally legal now does not mean that we (i.e. internet users as a whole) should just lay on our backs and let $BIGSITE have its way with us.

In fact, the uses of proxies that you seem to be pointing out as examples of why ubiquitous encryption is a "bad thing" - such as those in schools, homes, workplaces, etc. to block "objectionable content" - would probably be better handled by blocking IP addresses or domain names, rather than trying to break into encrypted HTTP sessions, would it not? Last I checked, TLS does not prevent the ability to detect when a user agent attempts to access a particular host (whether by IP address or domain name), thus allowing $BIGSITE to close off access to blacklisted or non-whitelisted hosts without needing to know the exact data being exchanged.

Honestly, and with all due respect, the idea that ubiquitous use of TLS would in any way, shape, or form stifle $BIGSITE's ability to monitor and block attempts to access "objectionable" sites seems absurd when there are plenty of more effective ways to do such things that don't involve a total compromise of privacy or secrecy.