Most people are running Windows. That means most people trying to learn how to program are running Windows. I wouldn't want to figure out how to set up a web server on Windows myself, and absolutely wouldn't expect someone learning to program on their own to be able to art it up without getting frustrated.
Even for people on Mac and Linux, having to start by learning the terminal is a pretty big and unnecessary obstacle to just getting to writing some JavaScript. Sure, you and I think it's easy, but it's a completely different paradigm which requires practice to get comfortable with.
Even if you can be there right by someone learning to program, and help them set up a web server, they will have to remember how to do that when they want to play with programming while you're not there. That's actually quite a lot to remember when you don't yet understand what the commands mean; you think of it as "go to the directory, start SimpleHTTPServer", but they have to memorize the text they have to type. Maybe you're the one who cd'd into the correct folder for them, and they remember to type `python -M SimpleHTTPServer` in the terminal you created; they will then have problems they don't know how to solve when they go home and open a terminal and type the command and it doesn't work because they weren't in the correct directory.
Absolutely, I don't think we are in disagreement at all. I just wanted to mention the availability of simple web servers (on Linux, as you rightly state).
On topic, I agree that this is throwing the baby out with the bathwater. A compromise would perhaps be an explicit whitelist of allowed directories to serve via the file:// protocol, set by the user (while disallowing traversal upwards of these, of course).
Even for people on Mac and Linux, having to start by learning the terminal is a pretty big and unnecessary obstacle to just getting to writing some JavaScript. Sure, you and I think it's easy, but it's a completely different paradigm which requires practice to get comfortable with.
Even if you can be there right by someone learning to program, and help them set up a web server, they will have to remember how to do that when they want to play with programming while you're not there. That's actually quite a lot to remember when you don't yet understand what the commands mean; you think of it as "go to the directory, start SimpleHTTPServer", but they have to memorize the text they have to type. Maybe you're the one who cd'd into the correct folder for them, and they remember to type `python -M SimpleHTTPServer` in the terminal you created; they will then have problems they don't know how to solve when they go home and open a terminal and type the command and it doesn't work because they weren't in the correct directory.