OK, so... you have people who with forethought and malice planned on raping Buffy... and you compare them to one person, who had been just told Buffy cared about him, who was convinced he was going to prove to her that she loved him... What he did was UTTERLY unacceptable, and YES I do class it as an assault of a sexual nature... so on a jury, I'd vote 'guilty'.
That said, this isn't a normal situation. Lack of a soul, is a reduced capacity - one Spike hasn't recognized until right then.
This is a person without a moral compass but with a wealth of feeling for the victim -- and no actual ill intent, in spite of what he did. (Bear in mind they had an ongoing, mutually violent, boundary-less relationship). This is an utterly out of control RELATIONSHIP. She almost beat him to death and he almost raped her. They are like two low-bottom addicts.
If that night had ended with him being fought off and unrepentant, then, anyone wanting to dust him, would have had no problem convincing me to do it. Instead (and please go back and watch that scene critically and consider who is speaking here -- I'm a child sex abuse survivor and I've had an attempted sexual mauling by an acquaintance that I fought off, so I actually know the situation a bit more than some. I hate rapists, and believe they often deserve the death penalty more than people who kill. Because every sex assault victim gets a life sentence.) So, when I tell you what I saw is more complicated than 'attempted rape', please consider how I feel about those who assault anyone sexually.
What I saw (and I think a lot of Spuffy fans saw that too) is a desperate, out of control man, in a messed up relationship who loses control and who, WITH NO SOUL TO GUIDE HIM... (Do REMEMBER THE RAVENING MESS ANGEL IS WITHOUT HIS SOUL??) Spike makes a horrible hash of what should have been a discussion in a calm situation....
Because he has no soul. Because his love, no matter how big is not enough.
What makes this different from the other attempted rapes in Buffy.... Spike's IMMEDIATE REACTION TO HIS OWN BEHAVIOR.
Horror.
He went and got his soul -- that needed moral compass -- BECAUSE of his horror about what he did. That is a very powerful message.
Then we come to season seven. They didn't immediately fall into each other's arms. It wasn't 'all better'. His once positive relationship with Dawn has been destroyed. In fact, he and Buffy are wary around each other, and though it is clear she forgave him (maybe even before he went for his soul -- b/c she took Dawn to his crypt for protection) it took time to HEAL, to become friends. He had to earn her trust, friendship, and eventually, love.
In arc of the series, it took until season ten for them to finally be in a stable relationship... This is not immediate magical redemption -- this is two screwed up people growing up and dealing with their issues. If you think that doesn't happen in the real world, you would be wrong. I know more than one recovering addict who, once they got their mind clear and made amends to their significant other (sometimes for horrible stuff) was able to rebuild a life with that person... with family.
Not having a soul is (IMO) worse than an addiction. Addicts know right from wrong... they just are under the sway of something more powerful than their moral compass... kind of like the demon. But they have that moral compass arguing with their addiction. Spike's moral compass is Buffy... but what he wants most is Buffy.
Anyway, their arc of healing to me, is one heck of a message. It isn't a neat, tidy message. It's not black and white. But it is REAL. LIFE is not black and white, folks. Life just is. In my opinion, the Buffy and Spike arc is a message that two messed up people could and did heal. One could argue that they healed each other. Buffy would be dead if it wasn't for Spike in season 6 (OMWF and maybe Death Things too). Both Spike and Angel became better people because of having Buffy in their lives. That makes Buffy one heck of a woman, as far as I am concerned.
Buffy is NO victim here. She is a true survivor.
That's the message. I don't think that's one of victimhood or easy outs. I think Buffy will make a lot of people think about what they want in a relationship that is problematic... and whether there's a possibility of true change. Most times in a bad relationship, there isn't, but sometimes, especially with younger people, and especially if both people are willing to get help for their issues (including addiction and a history of childhood abuse of any kind) there is a chance for healing and growing up.
I would not advise anyone under 15 to watch Buffy alone. If they did watch, it should be with a parent or adult who intended to discuss it with them frankly. I know I was abused as a child... maybe if someone had watched a show like Buffy with me when I was 12 or 13 and beginning my arc of misery and addiction, I might have been able to talk about it, instead of keeping it mostly a secret until I was 26 and nearly killing myself with my addiction.