Maciej Soltysiak:
The problem with his argument is that the web (and any protocol, really) needs a way to demand a hard guarantee that a request must proceed over a secure transport layer. If that layer is not available, the request must fail. Anything short of that is opportunistic security, and by definition not effective against an active attacker**.
I suspect what Tim Berners-Lee is actually annoyed with is Mixed Content Blocking and its tendency to impede upgrade to HTTPS rather than encourage it (due to blocking HSTS-upgraded URLs and addon redirect HTTPS upgrades as if they were HTTP URLs, rather than allowing them to be treated as first-class HTTPS urls). With that, I sympathize. Mixed Content Blocking seems to be doing more harm than good in terms of encouraging HTTPS transition, and has forced HTTPS-Everywhere to have to disable thousands of HTTPS upgrade rules due to site breakage from improperly blocked "Mixed Content".
Unfortunately, it seems that conflating the Mixed Content Blocking issue with the HTTPS namespace issue will likely distract the standards community long enough to delay development of proper solutions to HTTPS migration (like an improved form of HSTS that addresses known issues with Mixed Content Blocking: https://w3c.github.io/webappsec/specs/upgrade/).
Forgive me if I do my best to avoid this distraction myself.
** Sure, there could be a pile of new attribute flags that could be set on every HTML resource tag that says the resource must use a "secure http:" channel if the parent document happened to load over a secure channel, but the net engineering effort of deploying that correctly far exceeds the effort needed to mitigate the namespace fragmentation issues that Tim Berners-Lee is seemingly so concerned about.