Yes, Spike did chose it, and that's critical for his growth. But Buffy told Angel she couldn't risk him, and she chose not to wear it herself. Faith could have worn it - as could Dawn. Obviously Wiilow could and Anya. Hell, we've seen Giles work magic.

I really believe Spike knew absolutely that he was going to die, and delighted in it - finally Buffy would survive an apocalypse, and besides he was her chosen champion. But come on - sudden appearance of magical amulet from a dark and not remotely trustworthy source. Like Giles says earlier "Mist, graveyard, Halloween, this should end well." If Buffy didn't know he would die she was rationalizing. She knew Angel would, so she sent him away, YMMV.

Buffy didn't exactly sacrifice Spike but she chose him knowing he would die. He was more than willing to do so. But she allowed him to be the one to die when there were other options never looked at. Doylist - works great and very much needed on many levels. Watsonian - let's just say it leaves gaps to be filled (where stories are born). As a Spangel fan - and not just sex but who they were and who they are now - I am quite happy for everything thereafter.