| that's more secure, but still not bulletproof: A MITM (e.g. a router along a multi-hop route between the victim client and StackExchange) could silently drop the unsafe HTTP requests and maliciously repackage it as an HTTPS request, thereby circumventing the revocation. Also: even if an insecure HTTP request isn't dropped / makes it through to StackExchange's endpoint eventually (and thereby triggering the API key revocation), a MITM with a shorter trip time to SE's servers could race for wrecking havoc until the revocation happens. Nevertheless, SE's revocation tactic contributes positively to a defense in depth strategy. |
This approach is a practical choice based on the reality that the bulk of unencrypted traffic is not being actively mitmed and is at most being passively collected. Outside of actually developing cryptosystems, security tends to be a practical affair where we are happy building systems that improve security posture even if they don't fix everything.