Like most kids who grew up with Harry Potter, I used to have it in my head that their were distinct morals corresponding to the four Houses. Slytherins were bad. Everyone else was good. These were the facts of my childhood and that of millions of others. This great generalizing of people into black or white shades of personality and values. As I know now, that is not okay.
Therefore, when I took the Pottermore quiz in my freshman year of college, I was shocked to find out I had been placed in Slytherin House. This was the House that sired Draco Malfoy, Bellatrix Lestrange and Voldemort. It was a House with a reputation of churning out what is essentially magical Nazis. It was the House that needed to be entirely locked up during the battle of Hogwarts because they wouldn't fight the Death Eaters. The realization that being placed in this House would make people think I was an awful person struck me hard, but not soon after, I decided that I was proud to be in Slytherin.
JK Rowling has reassured people placed into Slytherin that it is an honorable House and that they value very admirable traits. As I recall, she even adds a little video at the big reveal of your House to let you know that you should not start sobbing uncontrollably. No other House has this video. However, it is important to acknowledge that her portrayal is the reason people fear being in this House in the first place. A House that gets a bad rep for seven straight books.
I strongly believe that there should have been a redemption arc for Malfoy akin to Zuko from Avatar: The Last Airbender. Draco deciding to screw his dad and join Harry in the big battle of Hogwarts would have been a great opportunity to show some of the good ways a person can be a Slytherin. By using his cunning and resourcefulness to switch sides when nobody was expecting it. Not even Voldemort! I also wished there had been a more positive representation of Slytherins in the story in general. All we really got were people who were selfish or downright evil. While Snape is supposed to be that positive representation, he was still a bully and slight stalker..... not great.
When you think about it, the traits that Slytherin values are traits that can get you far in life and ones you should be proud to possess. Cunning, ambition, resourcefulness. These are things that would sound great in a job interview when you think about it. I feel as if most Slytherins would make amazing business majors. While those characteristics help shape power hungry dark wizards, they also help shape successful young professionals. Bravery, wisdom, and kindness can get you far, but Slytherin traits will get you to where you want to be. You should not be ashamed to be cunning or ambitious. And you should not be ashamed to be a Slytherin.