My pragmatic view of HTTPS versus caching
One of the criticisms of going all HTTPS on the web is that it pretty much destroys caching. As Aristotle Pagaltzis commented on my entry, caching somewhat obscures traffic flow by itself (depending on where the cache is and who is watching), and as other people have commented in various places (cf), caching can serve valuable bandwidth reduction purposes. I and other people advocating an all HTTPS world should not ignore or understate this. On the contrary we should be explicit and admit that by advocating all HTTPS we are throwing some number of people who use caching under the bus.
The problem is that there is no good choice; regardless of what we choose here someone is getting thrown under the bus. If we go HTTPS and lose caching, we throw cache users under the bus. But everything that stays HTTP throws a significant number of other people under the bus of ISP traffic inspection, interception, tampering, and general monetization through various means. Our only choice is who gets thrown under in what circumstances, and what the effects of getting run over by the bus are. We cannot in any way pretend that there are no downsides of staying with HTTP, because there clearly are and they are happening today.
The effects of losing caching are mostly that for some people web browsing gets slower and perhaps more expensive due to bandwidth charges. The effects of losing privacy and content integrity are that for lots of people, well, they lose privacy, have their activities tracked quite intrusively, have advertising shoved down their throat and sometimes have their browsing weaponized and so on.
Faced with this tradeoff, I pick throwing people using caching under the bus of slower access. Sorry, cache users, I regret that you're going to have this happen to you (at least until people develop some more sophisticated HTTPS-capable caches and systems), but as far as I'm concerned it's clearly the lesser of two evils (as seen from my position, which is biased in some ways).
(I will not go so far as saying that cache users who insist that everyone else continue to have traffic intercepted, monitored, and monetized in order for the cache users to have an easier time are being selfish, partly because of the cost issues. But sometimes I do sort of feel that way.)