Mika, you're an idiot. You clearly have no clue what "bandwidth theft" is. If I inserted your graphics/video/etc into my site, loading them off YOUR server, THAT is "bandwidth theft". I've HAD people do that, placing graphics on their site that load directly off my server rather than just copy them and save them to their own server. Displaying an ENTIRE site framed by your own is not "bandwidth theft". Even if everyone in the world (for some strange reason) decided to access Facebook via a page in my blog, they would still be visiting Facebook, just in a smaller window. So in fact, you ARE "sending people to that site" (but as you already note, is easily thwarted with "anti-frame" scripts.)
If a COMPLETE remote site appears in a Window, content, advertisers and all, how is that "bandwidth theft"? Like someone is going to see "Facebook" inside my site and think, "Gee! I didn't know this guy owns Facebook!" If someone clicks an advertisers link on the Facebook page, does Facebook not still make money? Do you actually believe people will visit my site just to access Facebook or YouTube?
You said, "If they want you to do it, they'll tell you how". THEY DO. Facebook & YouTube LOVE embedding. Facebook has plugins for using their Commenting system and Albums. YouTube provides Embed Code for every video. That is closer to "bandwidth theft" than anything else. YouTube does not "provide code to embed an entire page" because all it takes is to display the URL in a window. There's no widespread need for users to do that.
I could, in theory, embed every YouTube video in my collection on a single Page and "steal" a LOT more bandwidth. "They probably do not" have the API structure or the CSS to handle this? I severely doubt you have any inside info of what YouTube "rather you not" do. Do you REALLY think loading index pages eat up more bandwidth or would cause more of a "slowdown" than if I created a page with 100 embedded videos on it?
And "nefarious peoples" can always find a way to do what they want anyway. They don't need WP to do that.
But as I told "fonglh", "Facebook" and "Youtube" are the least of my concerns. I'm more interested in multiple Post pages.