There's two different problem domains here that people keep stubbornly insisting on solving with the same technology.
1. I care about the identity of the other station. This does require a full PKI (or something like it)
2. I don't care about the identity of the other station I just don't want some third-party rando listening in. This is the majority of my web traffic, personally: I don't trust ycombinator.com any more than I would trust someone pretending to be ycombinator.com, so the verification that they are ycombinator.com doesn't actually do anything. Just encrypt opportunistically, everywhere, and leave the PKI for situations where it actually matters (like, if I were applying to ycombinator or something).
1. I care about the identity of the other station. This does require a full PKI (or something like it)
2. I don't care about the identity of the other station I just don't want some third-party rando listening in. This is the majority of my web traffic, personally: I don't trust ycombinator.com any more than I would trust someone pretending to be ycombinator.com, so the verification that they are ycombinator.com doesn't actually do anything. Just encrypt opportunistically, everywhere, and leave the PKI for situations where it actually matters (like, if I were applying to ycombinator or something).