I believe the beauty in blood, comes from several things. The primal urge of hunting. As it has been stated, some people feel more alive when coming into contact with it. This is probably because blood is a major source of life in our species.
Love has a stronger connection with blood, than most people might think, as it triggers most if not all romantic reactions.
Blood is the Primal Beauty of Love, Life, Death, Lust, and more. Saying it's not would be a lie. Though it is considered taboo, it was only deemed that way because society said so. But, in a primitive state, it could be whatever you want it to be.
If I had a girlfriend, and she wanted us to share blood, I'd be timid about it, but I'd likely be willing. Maybe mild resistance, as I lean more towards the feeling of vulnerability, in a relationship, than I would feeling powerful. Feeling like my partner's prey, has a bit of an exhilarating vibe to it. Who knows, maybe it gives my blood a better color or taste, with a hint of fear in it? I wouldn't go out of my way to find someone, who wanted my blood, or who wanted to share her own. But I wouldn't be against dating someone like that. (Sorry if this part is off topic, a bit...)
I definitely see the appeal in blood. It is beautiful in many ways. But I'd say sharing blood, if anything should be done with someone truly special. A partner that means something dear to you. Sharing blood is definitely taboo, but if done with someone you truly love, it could be the most primal way to show your love and devotion. It could mean everything, in your relationship. Blood is beautiful.
Looking for love in all the wrong places... Hopefully, she'll find me.