After Hermione's pureblood revelations, Malfoy went to the library to sort out his emotions. He hadn't done a terribly good job of hiding them back in the kitchen, and he blamed his continued exposure to mushy, touchy feely Order members for that weak moment. Perhaps they were driving him a bit mad.
Either way, now Draco was left to figure out alone what this meant for him, his beliefs, and his family. If what Hermione had said was true, how could he marry a pureblood and continue his family line without risking wiping out magic? It would be an insane thing to do… almost as insane as marrying a halfblood, or worse, a mudblood.
So deep was Draco in his thoughts that he didn't notice Hermione come into the library. She looked at him, still extremely pale, drumming his fingers on the table, looking lost in thought. "You know, Malfoy, this isn't the end of the world. No one's saying you have to kill yourself or anything."
"Oh, but they basically are. I have to taint my blood, blood that's been pure for centuries. Haven't you seen the Black family crest around here, Granger? Toujours Pur? Always Pure? These people are my mother's family."
"That's just what I'm saying, Malfoy. The Blacks and the Malfoys, the Parkinsons, the Weasleys… all of you are cousins! Even if this gene didn't exist, isn't the thought of marrying family a little disgusting?"
"That… I've never thought of it like that. It's not like we all have Sunday tea together. It's not like we've grown up raised as brothers and sisters. Our families aren't really close, unless you count those heart-warming Death Eater meetings."
"Emotionally close or not, you're genetically close. It's gross, seriously. Muggles would find you disgusting." It was at this point that Hermione began to wonder if she had crossed an unwritten line. She had. Malfoy stood up, his face actually red with anger.
"And just what the bloody hell are you insinuating, Granger? It's my blood that's pure here, not theirs. They're not even magical! They have to go about their daily lives, doing everything by hand. They have to make up ridiculous things like cars to get themselves around, they even have to clean by hand. It's filthy!"
"And just how do you know all this? Have you been reading some of these books about muggles I've got in here? Because you seem awfully knowledgeable."
"Well…" Malfoy stammered, because he had, in fact, been reading the books on muggles. "It's research! You have to know your enemy… and all that…" He stammered. "Listen, it's none of your business what I read. The point is that they're filthy and beneath us."
"They're actually quite smart, they have made their lives fairly easy considering they don't have magic. I never knew any better before I was at Hogwarts. I still do things the muggle way quite often, in fact. You get more of a sense of accomplishment from it." Malfoy stared at her as if she had been possessed.
"How in the hell can you stand there with a straight face and tell me that the muggle way of doing things is better than magic? That's just crazy! Besides, we're not arguing about that. We're arguing about the fact that you're saying I'm going to have to marry someone who is filthy and beneath me. It's unfathomable!"
Hermione had taken just about all she was willing to take in the name of showing the light to Draco Malfoy. It was with this in mind that she did what she did next. Perhaps it was mixed in with a slight bout of temporary insanity. Later, she couldn't explain why she'd done it, only that she wanted to shut Malfoy up about how different halfblood and mudblood and pureblood all were. So… she kissed him. But the thing about it was, he actually kissed her back…
