I understand that this idea has gained currency over the last decade, but I still don't understand or agree with it.
> If The Onion has a problem with the amount of data they are serving, perhaps they should configure their server to reject those requests; putting the onus on the end user not to issue HTTP GET unless a certain non-technical context exists seems.... odd.
No clue what you're talking about. For one, we're talking about website creators here rather than end users, and it's these website creators' failure to issue an HTTP GET that's considered bad manners.
I understand that other people have made up this idea that "hotlinking" is bad, but it never made any sense to me and I never got on board that train. People "hotlink" stuff off my blog all the time and I think that's great. I put the photos up there to be looked at; if people want to share them, I read that as a sign that I took a good photo. If I wanted to stop people from looking at my photos in certain ways - when the referer comes from a site other than my own, for example - then I would configure my web server not to serve out the bits under those conditions.
If the Onion doesn't want to serve out their CSS file under certain conditions, they should configure their server not to serve the bits under those conditions. If the Onion chooses instead to configure their web server to serve the bits to anyone who asks for them, people should feel free to ask for them.