Robert,
The current English error message text that I see from Python reads:
our error message system became overkill, with all those nice designs and multiple languages. in certain cases serving that message too certain requests caused gigabits of bandwidth. it is also not practical to update it with policies, because, um, it has all those nice designs and multiple languages.
we may actually end up having better error messages at some point in the future.
Everything except the very last line of that is either irrelevant or wrong. And ERR_ACCESS_DENIED, though vaguely informative, provides no detail about what happened or how to do things properly.
I agree.
This is bad enough for bot operators who are likely to be fairly intelligent people, but if we are going to give this to everyone with a missing user agent string too (which includes people behind poorly behaved proxies and people who use certain anonminizing software out of intense desire for "privacy"), then this kind of response really starts to send the wrong message.
We're not sending this response to missing UAs, as this response is being sent by Squid ACLs, and the UA check is done at the MW side.
Domas