After Buffy closed the door in his face, Giles went looking for Willow. Surely he could make the smartest of the group see reason. Then Willow could convince Buffy.
It didn't go quite as he planned.
Willow sat listening to him, let him make every point. Then she stood and walked toward the door. With her hand on the knob, she turned to him and spoke. There was no venom in her voice, just a deep sadness that the last innocence of her childhood had been lost.
"You are not the good and powerful Oz, Giles. You are the little man sitting behind a curtain. A curtain you've been building for so long, you've forgotten that it's only your creation. That world you live in, Giles, it's not real. The world is not black and white, its not even shades of grey. It's a bright, beautiful world filled with color.
"What we do here, its not playing. It's fighting for our lives - every day. Sometimes we fight monsters and sometimes we have to fight our own demons. We do the best we can. The best we can includes Spike. It has for quite some time. I get that you don't see it, I do. But that doesn't give you the right come in at the last minute and choose who we trust. We trust Spike; he's earned it. More than you have - you left us to fend for ourselves, Spike never did. If you don't like it, well then… its not Spike who should leave."
She turned and left him there, closing the door quietly behind her.