> Since a web server, by its primary mode of operation, does indeed more or less indiscriminately send replies to whomever makes a request, it follows that the duty of choice lies with the client.
Sorry, why isn't it the duty of choice the server owner, who chooses to put the server online in the first place? What exactly are these rules you think exist? This is the first time I've ever heard of them.
> Since a web server, by its primary mode of operation, does indeed more or less indiscriminately send replies to whomever makes a request,
This is completely false. The server owner can authenticate GET requests and return an unauthorized response if the client is not permitted to access the document. We are not talking about a situation where a hacker attempts to brute force a password or gain unauthorized access to a server. If the server is on the internet serving anonymous GET requests with no authentication the reasonable assumption is that anyone is permitted to access the data.