I simple line of "people once thought all Drow were evil, then we met Drizzt" would be a good start. And then a continuing ribbon of conversation spread throughout about the concept of nature vs nurture.

I think the solution is easier than everyone is making it out to be. The drow should be discussed as a Culture, not a race or a species. Just like among humans we are all one human race but there are different cultures...some cultures may have a majority of 1 skin tone vs another due to geological location but the culture is never ONLY one skin tone and one skin tone is never ONLY one culture. There are cultures throughout history that could be described as evil, often based on a diety they worshipped that did things like child sacrifice (etc.). A culture developed underground, like the drow, would be separated primarily from the world at large and it would be easily conceived how influenced those born into that society and not exposed to other options would fall into that culture and way of thinking. Drizzt, to me, has always stood for and represented the very proof that it is not because they were born drow that they were evil, he shows everyone its about your influences and your choices not your birth. The whole thing is simply Nature vs. Nurture.