One thing to keep in mind is that when Neptune and Uranus committed suicide to get the artifacts needed for the Grail they were proven both right and wrong.
Yes, sacrifice was needed. But until that point they had been eager to sacrifice. Being confronted with sacrificing themselves brought them up short. Not for long, they made that sacrifice knowingly and willingly, but it still exposed the hypocrisy. That it's alright to sacrifice so long as someone else pays the price.
Contrast this with Usagi, and the Inners, who are clear they will sacrifice, yes, but they will not sacrifice someone else.
Yes, sacrifice was needed. But until that point they had been eager to sacrifice. Being confronted with sacrificing themselves brought them up short. Not for long, they made that sacrifice knowingly and willingly, but it still exposed the hypocrisy. That it's alright to sacrifice so long as someone else pays the price.
Contrast this with Usagi, and the Inners, who are clear they will sacrifice, yes, but they will not sacrifice someone else.