I like Spike as a character a LOT, but I am one of the first people to admit that he was a threat to everyone in the beginning of Season 7, so I can understand why Giles and other characters were skittish about him being around.
True, it was dangerous. There's no getting around that. Spike was definitely dangerous when the First triggered him, and I understand Giles' concern. I even understand Wood's desire to kill Spike, because that was personal. But Giles undermined Buffy's authority in doing what he did. She made a decision, he thought she didn't make a good enough one, and he went behind her back to do what he wanted to do.
He's always telling Buffy to lead, to accept her calling, yet he doesn't follow her once she does? He doesn't trust the decisions she makes after he's pushed her into the leadership role? Giles should have trusted Buffy's judgment. It was just too easy for him to write off her beliefs and her decisions and go his own way. And ultimately, if Wood had succeeded, the world could have possibly ended. Buffy may have been making her choice based on emotion, but saving Spike was the right thing to do. Either no Champion would've been around to save the world, or Angel would've had to. And then Angel wouldn't have been able to do his own world-saving back on his show.